Population Density

Correct answer: B. 300 square kilometres

Explanation: Population density means the number of people living in one square kilometre. It connects total population with total area through the relation \(Density=Population/Area\). Therefore, when population and density are known, area is found by dividing population by density. The unit of the answer will be square kilometres because people cancel in the division.

Here, \(Area=90000/300=300\) square kilometres. Thus the region covers 300 square kilometres, so option B is correct. Option A would result from using an incorrect division, while the larger values do not match the given population and density.

Correct answer: C. 20000

Explanation: Arithmetic population density tells us how many people live, on average, in one unit of area. To find the total population, multiply density by area, provided both measurements use compatible units. Here the density is 80 persons per square kilometre and the area is 250 square kilometres. The square-kilometre units cancel, leaving a number of persons.

The calculation is \(Population = Density \times Area\) and \(80 \times 250 = 20,000\). Therefore, option C, 20000, is correct. The other numbers do not result from this multiplication. For example, dividing by 250 or using only one of the given values would not represent the population-density relationship. The result is an average population total for the stated area.

Correct answer: D. 200 persons per square kilometre

Explanation: Population density is calculated by dividing population by area: \(\text{density}=\frac{\text{population}}{\text{area}}\). Here the population is 120,000 and the area is 600 square kilometres. Dividing gives \(120000\div600=200\). Thus there are 200 people, on average, in each square kilometre. The correct choice is D.

The calculation can also be checked by noting that 600 multiplied by 200 equals 120,000. The unit must be persons per square kilometre because people are being divided by square kilometres. Choices A, B, and C result from using an incorrect divisor or an incomplete calculation. The answer is not the total population; it is the number of people associated with each unit of area.

Correct answer: A. Where many people live in a small area

Explanation: Arithmetic population density measures the average number of people living in each unit of total land area. The relationship is expressed as \(D=\frac{P}{A}\), where population is divided by area. Consequently, density becomes high when a relatively large number of people occupy a relatively small area. This is an average measure; it does not mean that every part of the region is equally crowded.

Option A gives exactly the condition that raises arithmetic density: many people are concentrated within a limited area. Option B would usually produce a low value because the population is spread over a very large area. Permanent ice or complete absence of settlement does not by itself create high density. The important comparison is between the size of the population in the numerator and the size of the land area in the denominator.

Correct answer: B. Vast polar region

Explanation: A vast polar region generally has very low population density. Such areas usually experience extreme cold, long periods of darkness or severe weather, permanent or seasonal ice, and difficult conditions for farming, construction, transport, and everyday services. The correct answer is B because a large area may contain very few residents, so the number of people per unit of area remains small.

A dense metropolitan core, an intensively farmed plain, and an industrial corridor normally provide more jobs, services, transport links, or productive land. These features can support concentrated settlement. The question asks about general likelihood, not an absolute rule: polar regions may have research stations or small settlements, but they rarely support dense, widespread permanent populations.

Correct answer: C. They have the same average number of people per unit area

Explanation: Population density describes how many people live, on average, in one unit of land area. If two regions have the same density, their population-to-area ratios are equal. This tells us about the average concentration of people, not about their total population, birth rate, or total area.

For example, one region may contain 10,000 people in 100 square kilometres, while another contains 20,000 people in 200 square kilometres. Both have a density of 100 people per square kilometre. Thus, option C is correct. Equal population or equal area is not necessary.

Correct answer: D. A region with a large population can have low density if its area is very large

Explanation: Total population and population density describe different features. Total population is simply the complete number of people in a region. Density, however, compares that population with the size of the area, using \(Density=Population/Area\). Thus, the same population may be crowded in a small area or spread out in a very large area.

A region may have a large population but still have low density when its area is extremely large. This directly demonstrates that population size and density are not identical concepts, so option D is correct. Options A and B incorrectly use the word “always,” and option C is false because density depends on area.

Correct answer: A. On average 150 people live in each square kilometre

Explanation: A density of 150 persons per square kilometre is an average relationship between population and area. It does not mean that every small part contains exactly 150 people, because settlements may be unevenly distributed. It means that if the whole population were considered in relation to the whole area, the average would be 150 people for each square kilometre.

Therefore, option A is correct. Option B wrongly treats density as the total population, option C treats it as the total area, and option D confuses population density with family size. For example, a region of 10 square kilometres with this density would have an average population of \(150 \times 10 = 1500\) people. The word average is important.

Correct answer: B. No because density may be an average for the whole region

Explanation: A regional population density is usually an average, not a map showing equal settlement everywhere. It divides the total population by the total area. A region can therefore have a crowded city, fertile plains, or river valley alongside mountains, forests, deserts, or protected land with very few residents. The calculated value combines all these contrasting spaces into one number.

Option B is correct because a high average density does not mean every locality is equally crowded. For example, a region with most people in one urban corridor may still have a low-population rural or mountainous part. Option A wrongly treats the average as an exact local pattern. Option C is wrong because area is essential to the calculation, and option D confuses density with rainfall. More detailed measures, such as local or physiological density, may be needed to study particular inhabited areas.

Correct answer: C. The average ratio of population to area for the whole country

Explanation: National density is an average calculated for the entire country. It is found by dividing the country's total population by its total area, usually expressed as persons per square kilometre. If people are concentrated in a few cities and the remaining land has very few residents, this average combines both crowded and sparsely settled areas. It therefore describes the country as a whole, not each locality separately.

Option C is correct because it states the population-to-area ratio for the whole country. National density cannot reveal the exact density of every city or village; those require separate local calculations. It is also not the same as urban density, since rural and undeveloped areas are included in the national area. Thus a single national figure can hide strong internal differences in settlement concentration.

Correct answer: D. Density will increase

Explanation: Density depends directly on population when area is constant: \(D=\frac{P}{A}\). The population rises from 60,000 to 90,000, an increase of 30,000 people. The area remains unchanged, so the denominator is fixed while the numerator increases. Consequently, the number of people per square kilometre must become larger. In fact, the population becomes 1.5 times its original value, so the density also becomes 1.5 times its original value.

Thus, option D, density will increase, is correct. It cannot remain unchanged because the area is not changing and the population is changing. It cannot decrease or become zero. Exact new density cannot be calculated without the area, but the direction of change is certain from the given information.

Correct answer: A. Density will become half

Explanation: Density tells us how many people live in one unit of area. It is found by dividing population by area: \(D=P/A\). When the number of people does not change, increasing the area spreads the same population over more space. Therefore, each unit of area contains fewer people, so the density becomes half when the area becomes double.

For example, if population is 1,000 and area is 100 square kilometres, density is 10 persons per square kilometre. If the area becomes 200 square kilometres, density is \(1000/200=5\). Thus the new density is half of the original density, and option A is correct. Options B and D would require population to increase.

Correct answer: B. Density will remain the same

Explanation: Population density is the ratio of population to area, written as \(D=\frac{P}{A}\). If population and area both become twice their original values, the new density is \(D'=\frac{2P}{2A}\). The same factor occurs in both the numerator and denominator, so it cancels.

Therefore, \(D'=\frac{P}{A}=D\), and the density does not change. Option B is correct. For example, a population of 100,000 in an area of 500 square kilometres gives 200 people per square kilometre; doubling both gives 200,000 people in 1,000 square kilometres, which is still 200 per square kilometre. A change in density requires population and area to change by different proportions.

Correct answer: C. Density will become four times

Explanation: Population density is calculated by dividing population by area: \(D=\frac{P}{A}\). If the original population is P and the original area is A, the original density is \(\frac{P}{A}\). After the change, population becomes 2P and area becomes A/2. Both changes make the density larger.

The new density is \(\frac{2P}{A/2}=\frac{2P\times2}{A}=4\frac{P}{A}\). Thus the new density is four times the original density, so option C is correct. It is not merely double, because the denominator has also been reduced by half. Options A and B fail to account for both changes together.

Correct answer: D. Density will become one-fourth of the original

Explanation: Population density means the number of people living in one unit of area. It is calculated by dividing population by area. If the original population is P and the original area is A, the original density is \(P/A\). Both changes in the question affect this ratio, so they must be included together rather than considered separately.

The new population is \(P/2\), and the new area is \(2A\). Therefore, the new density is \((P/2)/(2A)=P/(4A)\), which is one-fourth of the original density. Thus, option D is correct. A common mistake is to notice only the halved population and choose option B, but doubling the area reduces the density once more.

Correct answer: A. A thematic map showing regions according to density values

Explanation: Population density is a spatial measure: it compares the number of people with the area they occupy. A thematic map is designed to present one important theme, such as population density, and can shade or label regions according to density classes or values. This makes it easy to see which areas are crowded and which are sparsely populated.

Option A is therefore correct. A road map mainly shows transport routes, a weather map shows atmospheric conditions, and a political boundary map without population data cannot show density by itself. Boundaries may still be used as a base on a thematic map, but the map needs relevant population and area information to communicate density.

Correct answer: B. highest population density

Explanation: A map symbol or shade must always be interpreted through its legend. If the legend says that a darker shade represents higher population density, increasing darkness means that more people live in each unit of area. It does not directly describe rainfall, total area, or the total number of people.

The darkest region therefore belongs to the highest population-density category. Option B is correct. A large region could still have low density, and a small region could have high density, so area and total population cannot be inferred from this shading alone. The conclusion follows specifically from the stated map convention.

Correct answer: C. Comparatively more people live per unit area

Explanation: Population density tells us how many people live, on average, in one unit of area. It is found by dividing total population by total area. Therefore, a high density indicates that comparatively many people occupy each square kilometre or other chosen unit. It describes a relationship between people and land, not the absolute size of the country.

Option C is correct because it states the direct meaning of high density. A high-density country need not always have a small area; it may have a large population, or both. High density also does not mean that every person lives in a city, since dense rural regions can exist too. Options A, B, and D use unjustified words such as “always” and “every.”

Correct answer: D. On average fewer people live per unit area

Explanation: Population density means the average number of people living in one unit of area. A low-density region can still contain people, villages, towns, or even some cities. The word “low” is comparative: it says that the average number of people per square kilometre is small compared with another place. It does not say that every part is empty or that the region has no urban settlement.

Therefore, option D is correct because it gives the precise meaning of low population density: on average, fewer people live in each unit of area. Option A is too extreme, while options B and C are not necessary conditions. A region may have a city and may be very large, yet still have low average density.

Correct answer: A. The region with population 40000 and area 200

Explanation: To compare population densities, divide the population of each region by its area. A region with fewer people can still be more densely populated if its area is much smaller. The important comparison is therefore people per square kilometre, not the total population alone.

For the first region, density is \(40000\div200=200\) persons per square kilometre. For the second, it is \(50000\div500=100\) persons per square kilometre. Since 200 is greater than 100, the first region has the higher density. Therefore, option A is correct. Option B has the larger population, but its people are spread over a larger area.

Correct answer: B. The region with density 150

Explanation: Density already states how many people live in each unit of area, so the given figures can be compared directly. A density of 75 means 75 persons per square kilometre, while a density of 150 means 150 persons per square kilometre. The second value represents twice as many people in the same unit of area.

Consequently, the region with density 150 is more densely populated, so option B is correct. The total area of each region is not needed because the densities have already been calculated using area. Option A has the smaller value, option C incorrectly treats unequal values as equal, and option D confuses calculating density with comparing density.

Correct answer: C. 100000

Explanation: Population density tells us how many people live in one square kilometre. When both density and area are known, total population is found by multiplying them. The units also confirm the method: persons per square kilometre multiplied by square kilometres leaves persons. Therefore, the required operation is density times area, not division or addition.

Using the given values, population is \(250 \times 400 = 100000\) persons. Thus, the correct answer is option C, 100000. A value such as 50000 would result from using an incorrect factor, while 125000 is also unsupported by the stated density and area. The calculation can be checked because \(100000 \div 400 = 250\), exactly matching the given density.

Correct answer: D. 300 square kilometres

Explanation: Area can be calculated when population and population density are known. Density means population per unit area, so rearranging the density relationship gives \(\text{Area}=\frac{\text{Population}}{\text{Density}}\). The units also confirm this: people divided by people per square kilometre leaves square kilometres.

Substitute the given values: \(\text{Area}=\frac{150000}{500}=300\) square kilometres. This means that 150,000 people distributed at 500 people per square kilometre occupy 300 square kilometres. Therefore, option D is correct. The smaller options would produce densities greater than 500 for the given population.

Correct answer: A. Large population and housing concentration on limited land

Explanation: Population density means the number of people living in a unit of area. City centres often contain many apartments, offices, shops, institutions, and services on a relatively small amount of land. When a large number of residents occupy that limited space, the number of persons per square kilometre becomes high.

Therefore, option A gives the correct reason: population and housing are concentrated on limited land. A city centre does not need to have a large area; in fact, its small area can contribute to high density. Option B reverses this idea, C is plainly false, and D is incorrect because rainfall alone cannot explain urban density.

Correct answer: B. Rugged relief and difficult accessibility can limit settlement

Explanation: Population density is affected by how easily people can live, work, travel, and build in a region. Mountain areas often have steep slopes, broken relief, narrow valleys, difficult transport routes, and limited flat land for farms, houses, and industries. Some mountain climates are also severe, which can make daily life and economic activity harder. These conditions do not make all mountains empty, but they can restrict settlement to valleys and accessible slopes. When few people live across a large area, the average density remains low. Hence option B is correct.

Option A is false because mountain regions can cover very large areas. Option C is false because mountains may contain rivers, springs, and lakes. Option D is also too general, since many mountains are not permanently ice-covered. The correct explanation identifies physical obstacles, especially rugged relief and poor accessibility, rather than claiming that every mountain has exactly the same climate or resources.