Questions

It is due to the deficiency of Vitamin A. Retinol which is present in vitamin A. Its deficiency causes night blindness. It is available in carrots. 

In terms of concentration of impurity (a.k.a impurity doping concentration, often abbreviated to doping concentration), from the highest to the lowest among the three regions of a bipolar junction, emitter, collector, and base are the correct order. The above order is independent of the type of BJT, npn or pnp

A rainbow is a natural spectrum appearing in the sky after a rain shower. It is caused by dispersion of sunlight by tiny water droplets, present in the atmosphere. A rainbow is always formed in a direction opposite to that of the Sun. The water droplets act like small prisms. They refract and disperse the incident sunlight, then reflect it internally, and finally refract it again when it comes out of the raindrops.

Groundwater is all the water that has penetrated the earth's surface and is found in one of two soil layers. The one nearest the surface is the "zone of aeration", where gaps between soil are filled with both air and water. Below this layer is the "zone of saturation", where the gaps are filled with water.