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Science MCQs

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Question 641 Hard

What is the melting point of a substance?

A
Temperature where it boils
B
Temperature where it melts
C
Temperature where it freezes
D
Temperature where it evaporates
Question 642 Hard

Which of the following is a chemical change?

A
Mixing salt and sand
B
Boiling water
C
Heating magnesium ribbon
D
Breaking glass
Question 643 Hard

What is the correct chemical equation for decomposition of water?

A
H2O → H2 + O2
B
2H2O → 2H2 + O2
C
H2O → H + O
D
2H2O → H2 + O2
Question 644 Hard

Which of the following is a physical change?

A
Burning of coal
B
Fermentation of grapes
C
Melting of iron
D
Corrosion of metal
Question 645 Hard

What is the chemical property of hydrochloric acid in stomach?

A
It is liquid
B
It is acidic
C
It is soluble
D
It has a low boiling point
Question 646 Hard

What is the main conclusion from Activity 5.3 where a candle is covered with a beaker?

A
CO₂ is needed for combustion.
B
Combustion produces water.
C
Oxygen is needed for combustion.
D
Nitrogen supports combustion.
Question 647 Hard

Which of the following statements about tarnishing is FALSE?

A
It is a surface phenomenon.
B
It only involves reaction with oxygen.
C
It can be caused by hydrogen sulphide.
D
It forms a dull layer on metals.
Question 648 Hard

What does the chemical equation 2H₂ + O₂ → 2H₂O represent?

A
Decomposition of water
B
Formation of water
C
Combustion of hydrogen
D
Both 2 and 3
Question 649 Hard

Which of the following changes is irreversible?

A
Melting of butter
B
Boiling of water
C
Burning of paper
D
Dissolving salt in water
Question 650 Hard

The chemical property 'acidity' is useful in:

A
Making electrical wires
B
Digestion of food in the stomach
C
Preventing rusting
D
Making alloys
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