Changes Around Us: Physical and Chemical MCQs for UPSC Prelims
120 practice questions covering Changes Around Us: Physical and Chemical, organised into 2 topics.
120 questions include a written explanation.
Pick a topic below, or try the samples first.
A potter shapes wet clay into a pot and then bakes it in a hot kiln. Why is this change made on purpose?
ATo make the pot dissolve away in water
BTo help the clay rust when it is left in the rain
CTo get a hard, useful pot that keeps its shape and holds water
DTo spoil the clay so that it can no longer be used
Show answer and explanation
Correct answer: C - To get a hard, useful pot that keeps its shape and holds water
Baking hardens the clay so that the pot keeps its shape and holds water, which is exactly why the potter does it. Nobody bakes clay in order to spoil it. Rusting happens to iron, not clay, and a baked pot is meant to resist water rather than dissolve in it.
Q2
medium
Which observation best shows that rust is a different substance from the iron it forms on?
ARust forms on the outer surface of the iron object
BRust is a brown, flaky powder that is neither shiny nor strong like iron
CRust appears only after the object has been left for many days
DRust makes the iron object look old and neglected
Show answer and explanation
Correct answer: B - Rust is a brown, flaky powder that is neither shiny nor strong like iron
Different properties mean a different substance, and rust differs from iron in colour, strength and shine. Forming on the surface, taking time to appear and looking untidy are all true of rust but say nothing about whether the material itself has changed.
Q3
medium
An aluminium sheet is cut and pressed into a lunch box. Which statement best describes this change?
AA chemical change, because a useful new object is made
BA change of state from solid to liquid
CA change of state from liquid to solid
DA change of shape and size only, as the metal is still aluminium
Show answer and explanation
Correct answer: D - A change of shape and size only, as the metal is still aluminium
Cutting and pressing alter the form of the sheet, but every property of the metal remains that of aluminium. The metal stays solid throughout, so neither of the change-of-state options can apply. Making a new object is not the same as making a new substance, which is what a chemical change requires.
Q4
hard
Assertion (A): A change in which one or more new substances are formed is called a chemical change. Reason (R): Chemical changes are often accompanied by a rise or fall in temperature.
ABoth A and R are true, and R is the correct explanation of A
BBoth A and R are true, but R is not the correct explanation of A
CA is true, but R is false
DA is false, but R is true
Show answer and explanation
Correct answer: B - Both A and R are true, but R is not the correct explanation of A
A states the correct definition of a chemical change, so it is true. Many chemical changes do give out or take in heat, so R is true as well. But a temperature change is only a common sign, not the reason for the definition, and it happens in some physical changes too, so R does not explain A.
Q5
hard
Which reasoning correctly explains why a rusted iron gate cannot be made as good as new simply by drying it in the Sun?
ADrying will reverse the change if the gate is left in the Sun for long enough
BRust must be cooled rather than dried in order to become iron again
CDrying works only on changes that were caused by heat in the first place
DRust is a new substance, and drying only removes water without turning rust back into iron
Show answer and explanation
Correct answer: D - Rust is a new substance, and drying only removes water without turning rust back into iron
Rusting produced a new substance on the surface, and removing moisture does nothing to change rust back into iron. It only slows down further rusting. Cooling has no such power either, and no length of drying will undo a chemical change, so waiting longer will not help.
Q6
easy
A sheet of paper is folded several times to make a paper boat. What has changed?
AThe chemical nature of the paper
BOnly its shape and size, not the material
CThe material, from paper to plastic
DNothing at all
Show answer and explanation
Correct answer: B - Only its shape and size, not the material
Folding rearranges the sheet but leaves it as the same piece of paper, so only the shape and the space it takes up have changed. Paper cannot turn into plastic by folding, and its chemical nature is untouched. Saying nothing changed ignores the obvious change of shape.
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