1,382 practice questions for CBSE Class 8 Science, organised by NCERT chapter (13 chapters). Every question includes a written explanation. Pick a chapter below, or try the samples first.
Assertion (A): The thinning of the ozone layer is the main cause of global warming. Reason (R): Ozone in the upper atmosphere absorbs ultraviolet radiation from the Sun.
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: D - A is false, but R is true
A is false, because global warming is caused mainly by extra greenhouse gases such as carbon dioxide trapping heat, which is a separate problem from ozone loss. R is true, since absorbing ultraviolet radiation is exactly what the ozone layer does. As A is false the first two choices go, and the third fails because R is true.
Q2
easy
A stick of chalk snaps easily, but an iron rod of the same thickness does not. This tells us that
Achalk particles move about much faster than iron particles inside the solid
Bthe attraction between iron particles is stronger than that between chalk particles
Cchalk has no particles inside it
Diron particles are much smaller than chalk particles, so they cannot be pulled out of place
Show answer and explanation
Correct answer: B - the attraction between iron particles is stronger than that between chalk particles
Breaking a solid means pulling its particles apart, so the harder material has the stronger attraction between its particles. Chalk is made of particles like everything else. Particle size does not decide strength here, and particles in both solids only vibrate in place.
Q3
medium
Consider these two statements about the Moon. (i) The Moon spins on its own axis. (ii) The Moon shows us the same face all the time. Which is correct?
ANeither (i) nor (ii)
BOnly (ii)
CBoth (i) and (ii)
DOnly (i)
Show answer and explanation
Correct answer: C - Both (i) and (ii)
The Moon does spin, and it also keeps one face towards us, so both statements are true. They fit together because one spin takes exactly as long as one trip around the Earth. Choosing only one of them misses that these two facts are partners rather than opposites.
Q4
easy
A block has a mass of $60\ \text{g}$ and a volume of $30\ \text{cm}^3$. Its density is
A$30\ \text{g/cm}^3$
B$1800\ \text{g/cm}^3$
C$0.5\ \text{g/cm}^3$
D$2\ \text{g/cm}^3$
Show answer and explanation
Correct answer: D - $2\ \text{g/cm}^3$
Density is mass divided by volume, so it is $60 \div 30 = 2\ \text{g/cm}^3$. Dividing the volume by the mass gives $0.5$, which is the common reversal slip. The value $30$ is just the volume copied down, and $1800$ comes from multiplying instead of dividing.
Q5
hard
If all the decomposers in a forest suddenly vanished, the most likely long-term result would be that
Anothing would change, since decomposers feed only on waste
Bdead leaves and remains would pile up and the soil would grow poorer in nutrients
Cplants would grow faster, because decomposers would no longer compete with them for food
Devery herbivore in the forest would die within a day
Show answer and explanation
Correct answer: B - dead leaves and remains would pile up and the soil would grow poorer in nutrients
Decomposers break down dead matter and hand its nutrients back to the soil, so without them the remains would collect while the soil slowly lost its supply of nutrients. Plants would suffer rather than benefit from that loss. The change would be large, not nothing, but it would build up over months, not kill herbivores in a day.
Q6
medium
A village depends on a stream that is fed by rainfall. If the rains fail for two years running, the most direct effect on the villagers is
Athe stream beginning to flow uphill
Ba rise in the oxygen content of the air
Cless water for drinking and for their crops
Da change in the length of the day
Show answer and explanation
Correct answer: C - less water for drinking and for their crops
The stream is refilled by rain, so a long dry spell leaves less water for homes and fields. Day length depends on Earth's rotation and is unaffected by rainfall. The oxygen in air does not rise because rain fails, and water cannot flow uphill.
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