Laws of chemical combination

Correct answer: A. It applies to several compounds of the same two elements

Multiple proportions needs same two elements and several compounds. Exam tip: check both conditions.

Correct answer: A. It applies to gas volumes at same temperature pressure

Gay-Lussac's law is based on gaseous volumes and same conditions. Exam tip: look for gases and same conditions.

Correct answer: A. Total mass → conservation of mass; pure compound → definite proportions; many compounds → multiple proportions; gas volumes → Gay-Lussac

Option A gives the correct sequence. The law of conservation of mass concerns equality of total mass before and after a reaction. The law of definite proportions applies to the fixed mass ratio of elements in a pure compound. The law of multiple proportions applies when the same two elements form more than one compound. Gay-Lussac’s law of gaseous volumes concerns volumes of reacting gases. In option B, total mass is incorrectly linked to Gay-Lussac’s law. Exam tip: match the clue words—total mass, pure compound, many compounds, and gas volumes—with their respective laws.

Correct answer: A. Conservation of mass

Unchanged total mass directly indicates conservation of mass. Exam tip: choose conservation when mass remains same.

Correct answer: A. Law of definite proportions

Elements in a pure compound are in fixed ratio. Exam tip: choose definite proportions from composition always same.

Correct answer: A. Law of multiple proportions

(NO) and (NO_2) are different compounds of the same two elements. Exam tip: look for simple mass ratio of different compounds.

Correct answer: A. Gay-Lussac's law of gaseous volumes

At same temperature and pressure gas volumes are in simple ratios. Exam tip: choose Gay-Lussac from volume ratio.

Correct answer: D. Conservation of mass means mass disappears

In conservation of mass mass does not disappear. Exam tip: watch for opposite meaning in wrong conclusions.

Correct answer: A. Whether the unit matches the law and the ratio is simplified

If unit and simple ratio are correct the answer becomes strong. Exam tip: final check reduces calculation errors.

Correct answer: A. 50 ग्राम (50 g)

By the law of conservation of mass, the total mass remains unchanged in a closed system. Thus, the product mass is 32 g + 18 g = 50 g.

Correct answer: A. 39 grams

This question uses the law of conservation of mass: in a closed chemical reaction, the total mass of the reactants equals the total mass of the products. Let the unknown reactant mass be x grams. Then 25 + x = 64, so x = 64 − 25 = 39 grams. Therefore, option A is correct. The value 25 grams merely repeats the known reactant, while 64 grams is the total product mass rather than the unknown reactant. The value 89 grams results from adding the two given numbers, but addition is inappropriate because the product total already equals the sum of both reactants.

Correct answer: B. 28 grams

The direct answer is B: 28 grams. The law of conservation of mass says that, in a chemical reaction, the total mass of reactants equals the total mass of products, when the gas is included. Here, total reactant mass is 48 grams. The solid product has a mass of 20 grams, and the remaining mass must belong to the gas. Calculation: mass of gas = total product mass − solid product mass = 48 − 20 = 28 grams. Option A, 20 grams, repeats the mass of the solid and ignores the remaining material. Option B is correct because it balances the total mass. Option C, 48 grams, is the total mass of all products together, not the gas alone. Option D, 68 grams, adds masses instead of finding the missing part and violates conservation of mass. The important exam step is to include invisible or escaping gas in the products. A gas has mass even if it cannot be seen. Remember: missing product mass equals total reactant mass minus known product mass.

Correct answer: C. 40 ग्राम (40 g)

The law of conservation of mass applies in a closed system, so the total product mass equals the total reactant mass: 13 g + 27 g = 40 g.

Correct answer: D. 20 ग्राम (20 g)

The known products have a combined mass of 52 g + 18 g = 70 g. Subtracting this from the total gives product C's mass: 90 g − 70 g = 20 g.

Correct answer: B. स्थिर अनुपात का नियम (Law of definite proportions)

The law of definite proportions states that a pure compound always contains its elements in a fixed mass ratio. The same aluminium-to-oxygen mass ratio in every pure Al₂O₃ sample illustrates this law.

Correct answer: C. स्थिर अनुपात का नियम (Law of definite proportions)

The law of definite proportions states that a pure compound has a constant composition by mass. Therefore, pure ZnS always has the same mass ratio of zinc to sulfur.

Correct answer: B. 33 grams

The fixed ratio A:B = 6:11 means that the masses must be multiplied by the same factor. Since A changes from 6 parts to 18 grams, the scale factor is 18 ÷ 6 = 3. Therefore, B has a mass of 11 × 3 = 33 grams, so option B is correct. The answer is not 22 grams, which would correspond to multiplying 11 by 2; 36 grams incorrectly doubles the given mass of A; and 44 grams would multiply 11 by 4. The governing concept is the law of definite proportions: a pure compound always contains its elements in a fixed mass ratio.

Correct answer: B. 25 ग्राम (25 g)

The ratio has 8 + 5 = 13 total parts. Each part is 65 g ÷ 13 = 5 g, so B, which represents 5 parts, has a mass of 5 × 5 g = 25 g.

Correct answer: D. 45 ग्राम (45 g)

The 4 parts for B weigh 20 g, so each part is 20 g ÷ 4 = 5 g. A represents 9 parts, so its mass is 9 × 5 g = 45 g.

Correct answer: A. 3:5

The mass ratio A:B is 27:45. Dividing both terms by their greatest common divisor, 9, gives 3:5. The ratio 5:3 reverses the order of A and B, so it is incorrect. Exam tip: simplify a ratio by dividing both terms by their greatest common divisor.

Correct answer: A. दोनों नमूनों में घटकों का द्रव्यमान अनुपात समान है

Dividing both terms of 12:16 by 4 gives 3:4. Therefore, the mass ratio of the components is the same in both samples, consistent with the law of definite proportions. The total masses of the samples need not be equal; only the component ratio must remain constant. Exam tip: reduce ratios to their simplest form before comparing them.

Correct answer: C. Lemon drink

The law of definite proportions applies to pure compounds, which have a fixed composition by mass. A lemon drink is a mixture whose proportions of ingredients can vary.

Correct answer: C. Ratio of silicon and oxygen in pure SiO₂

A pure compound has elements chemically combined in a definite and constant proportion by mass. Pure silicon dioxide, SiO₂, always contains silicon and oxygen in the fixed ratio determined by its chemical formula, so option C is correct. Soil, tea, and air are mixtures, not pure compounds; their amounts of sand, sugar, or dust can vary from sample to sample. A formula such as SiO₂ represents a definite composition, whereas a mixture has no single fixed formula and its components can be separated physically. Therefore, the governing concept is the law of definite proportions, and only the pure SiO₂ example satisfies it.

Correct answer: C. Law of multiple proportions

NO₂ and N₂O₅ are different compounds made from the same two elements. For a fixed mass of nitrogen, the oxygen masses that combine with it are in the ratio 32:80, or 2:5, a simple whole-number ratio. This illustrates the law of multiple proportions.

Correct answer: A. 2:5

The governing principle is the law of multiple proportions. Since the same mass of A, 9 g, combines in both compounds, the comparison must be made only between the corresponding masses of B. These are 12 g and 30 g, so the required ratio is 12:30. The greatest common divisor of 12 and 30 is 6. Dividing both terms by 6 gives 12 ÷ 6 : 30 ÷ 6 = 2:5. Therefore, option A is correct. Option B reverses the order of the compounds. Option C is not obtained by valid simplification, because 12:30 is equal to 2:5, not 3:5. Option D is also not equivalent to the given ratio. The fixed mass of A is what permits this comparison under the stated law.