Class 8 Practice – Level 3 – Set 1 – Combustion and Flame

Total questions: 15

Why is it difficult to ignite a lump of coal with a matchstick, whereas coal powder ignites easily?

Coal powder has a higher calorific value

Coal powder has a higher ignition temperature

Coal powder has a larger surface area exposed to oxygen

Coal powder is more chemically reactive than solid coal

None

Incomplete combustion of hydrocarbons produces carbon monoxide, which is poisonous. How does carbon monoxide affect the human body?

It reduces the production of red blood cells

It interferes with oxygen transport in the blood

It lowers blood pressure drastically

It causes rapid decomposition of hemoglobin

None

Which of the following best explains why spontaneous combustion can occur in oil-soaked rags left in a confined space?

The oil reacts with oxygen, causing the temperature to drop rapidly

The oil reacts with air, producing heat that accumulates

The rags cool down due to heat absorption

The oxygen concentration inside the confined space decreases significantly

None

Given two fuels, A and B, where A has a higher calorific value than B but produces more pollutants, which fuel would be preferable for long-term sustainability and why?

Fuel A because it provides more energy

Fuel B because it causes less pollution

Fuel A because it is cheaper to use

Fuel B because it has a higher ignition temperature

None

Explosions release a large amount of energy in a very short time. What is the critical factor that differentiates explosion combustion from rapid combustion?

Explosion combustion occurs at higher temperatures

Explosion combustion involves the presence of liquid fuels

Explosion combustion releases energy with sudden pressure increase

Explosion combustion produces carbon monoxide

None

Which characteristic of hydrogen as a fuel makes it challenging to use in conventional internal combustion engines?

Its low calorific value

Its highly explosive nature

Its high ignition temperature

Its non-polluting nature

None

Which of the following substances is essential for the complete combustion of a fuel?

Carbon dioxide

Nitrogen

Water vapor

Oxygen

None

In a situation where there is a gas leak in a kitchen, why is it recommended to avoid turning on any electrical appliance?

Electrical appliances increase oxygen levels in the room

Electrical sparks may ignite the flammable gas

Electrical appliances absorb the leaked gas

Turning on appliances increases the gas flow

None

Why does the outermost zone of a flame appear blue during complete combustion?

It has the lowest temperature

It undergoes incomplete combustion

It has the highest temperature and uses sufficient oxygen

It contains unburnt carbon particles

None

10.

Why does a matchstick ignite when struck against the side of a matchbox but not spontaneously in air?

The friction raises the temperature above the ignition point

The air has less oxygen

The matchstick contains inert materials

The matchstick’s ignition temperature is higher than room temperature

None

11.

How does the combustion of fossil fuels contribute to global warming?

By increasing the oxygen concentration in the atmosphere

By releasing large amounts of water vapor

By releasing carbon dioxide, a greenhouse gas

By absorbing carbon dioxide from the atmosphere

None

12.

Why is the calorific value of hydrogen significantly higher than that of coal, but hydrogen is still not commonly used as a fuel?

Hydrogen has a lower ignition temperature

Hydrogen is expensive and difficult to store

Hydrogen produces too much heat

Hydrogen is abundant but inefficient

None

13.

Why are dry chemical powder fire extinguishers more versatile compared to water and CO₂ extinguishers?

They can be used on all types of fires, including electrical and metal fires

They reduce the oxygen supply more effectively

They absorb heat more efficiently than water

They cause chemical reactions with the fuel

None

14.

Which of the following conditions is NOT conducive to spontaneous combustion?

Storing coal dust in an enclosed space

Accumulation of hay bales in a poorly ventilated barn

Wet rags soaked in linseed oil left in a pile

Metal objects left out in the sun

None

15.

Why is a non-luminous flame, like the one produced in a Bunsen burner, preferred in scientific experiments?

It has a lower temperature

It provides more light

It indicates incomplete combustion

It provides a steady, soot-free heat source

None

1 out of 15

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Class 8 Practice – Level 3 – Set 1 – Combustion and Flame

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