Variables in an experiment

Correct answer: B. Categorical variable

Light colors form distinct categories so this is a categorical independent variable. Values of a categorical variable do not represent continuous numerical intervals.

Correct answer: A. Quantitative independent variable

Sugar amount is varied numerically so it is a quantitative independent variable. Recording values with units makes the measurement clear.

Correct answer: B. It may be subjective and less precise

Terms such as good average or poor may depend on observer judgement. Use a clear numerical measurement where possible.

Correct answer: B. Initial temperature will become a confounding variable

Initial water temperature affects cooling time so changing it creates confounding. It should be kept constant.

Correct answer: A. The complete curve may be mistaken for a linear relationship

Only two early points can hide a nonlinear trend. Sufficient values should be tested across the full range.

Correct answer: B. It is usually true in experimental graphs but axis placement itself does not determine the variable's role

In experimental graphs the independent variable is usually placed on the horizontal axis. Its role is still determined by what was changed and what was measured.

Correct answer: B. Test the effect of length fairly

Keeping mass constant allows a clear comparison of the effect of length. Controlled variables reduce alternative explanations.

Correct answer: B. Convert both data sets to the same unit

Direct comparison of dependent-variable values in different units can be misleading. Convert all values to a common unit first.

Correct answer: B. Uncontrolled extraneous variable

Light also affects plant growth and is not kept the same here. It is therefore an uncontrolled extraneous variable.

Correct answer: A. It is more objective and quantitative

Measurement in centimeters is more objective and repeatable. A quantitative dependent variable with a clear unit gives better comparison.

Correct answer: B. Confounding variable

The governing concept is control of variables. Temperature is intended to be the independent variable and bacterial growth is the dependent variable, but incubation time also influences growth. Because incubation duration changes between temperature groups, its effect becomes mixed with the temperature effect. It is therefore a confounding variable, making option B correct. It is not properly controlled, a unit, or a replicate of temperature.

Correct answer: B. Measure and record it while keeping its variation small

The governing principle is transparent control of experimental limitations. If a controlled variable cannot remain perfectly constant, the researcher should measure and record it, keep its variation as small as practicable, and consider its possible influence when interpreting results. Hence, option B is correct. Ignoring the variation hides a possible source of bias, while relabelling the variable or deleting all results does not improve the investigation.

Correct answer: A. Keep sound intensity the same for all music types

The governing principle of a fair test is changing only the intended independent variable. Here, music type is the independent variable and reading speed is the measured dependent variable. Sound intensity could also influence reading speed, so it must be kept the same for every music type. Thus, option A is correct. Keeping reading speed or music type constant would defeat the investigation, and different passages would introduce another confounding factor.

Correct answer: B. दाग क्षेत्रफल में प्रतिशत कमी

When starting stain sizes are unequal, comparing only the final remaining area can be misleading: a larger starting stain may leave a larger area even after effective cleaning. Percentage decrease accounts for the starting value. It can be calculated as (initial area − final area) ÷ initial area × 100. Thus B gives a more comparable measure of cleaning performance; A alone does not fully correct the initial difference.