211: What are Rubies and Sapphires chemically known as?
(a) Silicon dioxide
(b) Aluminium oxide
(c) Lead tetroxide
(d) Boron nitride
Explanation:
Corundum is the mineral of which rubies and sapphires are varieties. The chemical symbol is A1203. When the corundum is red, it's a ruby. When it's any other color, it's a sapphire.
Not always a blue sapphire. Sometimes it's a yellow sapphire. Or a green sapphire. Or black, or pink, etc. They consist of aluminium oxide crystals containing impurities which dote them with their various tints: titanium and iron for the blue of the sapphire, chromium and vanadium for the red of rubies.
212: Which one of the following is a modified stem ?
(a) Carrot
(b) Sweet Potato
(c) Coconut
(d) Potato
213: Mulching the soil is a process whereby:
(a) Big pieces of soil are broken down into smaller pieces
(b) The field is irrigated at regular intervals
(c) Transplanting of seedlings take place
(d) Loose material, dung, etc. are laid on the ground to prevent excessive evaporation or erosion of the soil
214: Fat present below the skin surface in our body, acts as a barrier against
(a) loss of heat from the body
(b) loss of essential body fluids
(c) loss of salts from the body
(d) entry of harmful micro-organisms from the environment
Explanation:
Fat present below the skin surface acts as an insulator thus preventing exchange of heat from surrounding 'Blubber' a thick fat layer underneath the skin of 'whales' helps as 'thermoregulator'.
215: Mixture of which one of the following pairs of gases is the cause of occurrence of most of the explosions in mines?
(a) Hydrogen and oxygen
(b) Oxygen and acetylene
(c) Methane and air
(d) Carbon dioxide and methane
Explanation:
Mixture of methane, coal dust and air can produce a shock wave that travels as much as 6 times the speed of sound through the mine workings. Confinement is a physical factor to consider in the development of the explosion. The shock waves begins to occur as the expanding gases accelerate into the ambient air. This can be exacerbated in the mining environment because the paths of release are limited.