Explanation

Straw, camphor, alcohol, petrol, diesel etc. catch fire easily to release heat energy and light energy.

So, these are examples of combustible substances.

Explanation

Mercury is the only elemental metal that remains in a liquid state at room temperature (around 25°C).

It is used in thermometers, barometers, and other scientific instruments due to this unique property.

Four other elements are liquids slightly warmer than room temperature.

They are:

1. Francium
2. Cesium
3. Gallium
4. Rubidium

Explanation

CNG and Sui Gas have the same composition, primarily methane (CH₄).

Both are used as fuel for heating and vehicles.

Explanation

Group IIA elements (alkaline earth metals) have 2 electrons in their outermost s-orbital.

Their general electronic configuration ends with ns², where n is the period number.

Explanation

Explanation

Carbon has 4 electrons in its outer shell.

It forms 4 covalent bonds, making it tetravalent (valency = 4).

Explanation

The air in Earth's atmosphere is made up of approximately 78 percent nitrogen and 21 percent oxygen.

Explanation

In the Fahrenheit scale:

• The freezing point of water is 32°F
• The boiling point of water is 212°F

Explanation

Explanation

The element required for solar energy conversion is silicon.

Silicon is the most common semiconductor material: Silicon is used in about 95% of solar cells sold today. 

Silicon is a naturally occurring element: Silicon is the second most abundant element on Earth, after oxygen.