Explanation

Gallium melts at about 29.7 °C, slightly above normal room temperature.

Hence, it can melt in the hand, making it liquid near room conditions.

Explanation

Filler metal is added in gas welding to join two metal pieces and fill gaps.

It melts along with the base metal to form a strong welded joint.

Explanation

Amalgams are alloys in which mercury is a principal component.

They are commonly used in dental fillings and some industrial applications.

Explanation

Limestone (CaCO₃) is added to the blast furnace as a flux to remove impurities like silica (SiO₂).

It forms slag (CaSiO₃), which floats on molten iron and is removed easily.

Explanation

Argon is chemically inert and does not easily form compounds, a key property of noble gases.

It belongs to Group 18 of the periodic table, which contains all noble gases.

Explanation

Algae growth is more common in soft water as it lacks high calcium and magnesium content.

Hard water inhibits algae due to high mineral content.

Explanation

Silica dust affects the lungs, causing silicosis, a respiratory disease.

Other pollutants like Benzene and Lead affect blood and nervous system rather than lungs directly.

Explanation

Cast iron has excellent fluidity, allowing it to fill moulds easily.

It is economical and widely used for machine parts, pipes, and engine blocks.

Cast iron is the most commonly used metal for casting.

Explanation

Fatigue strength is improved by surface treatments, cold working, or shot peening, which induce compressive stresses.

Hot working, on the other hand, does not enhance fatigue strength and may even reduce it by softening the surface.

Hot working does not increase fatigue strength.

Explanation

Silica (SiO₂) is a naturally occurring oxide with high melting point and hardness.

It is widely used in glass, ceramics, and refractory applications.

Silica is classified as a ceramic material.