Questions

When their is a colloid in the solution, then it will show the Brownian movement, such as dust particle in the air will show the Brownian movement.

Hence, Brownian movement arises due to the impact of the molecules of the dispersion medium with the colloidal particles. It has been postulated that the impact of the molecules of dispersion medium on the colloidal particles are unequal.

This leads to the zig-zag (random) motion of the colloidal particles.

The main constituent of biogas is methane (55-70%), CO2 (30-45%) and some traces of gases such as H2S and ammonia.

Biogas is produced under anaerobic conditions; the process is denominated as anaerobic digestion.

An owl.

"What noise does an owl make?

The sound an Owl makes, it sounds like, "Who?" to our ears.

They sounds entire lives asking the same question, but they'll never give any answers.

Water has the maximum density at 4oC. So at this temperature, it sinks down to bottom and stays here. If it cools further, it will become less dense and move up. So while the upper layers can cool enough to form ice, the bottom layers remain as water at  4oC .  

Therefore, (C) is correct.