Questions

When water is cooled from 4°C to 0°C, its density decreases.

When water cools from 4°C to 0°C, ice crystals begin to form because the water is approaching its freezing point. When water freezes, the water molecules form a lattice that increases the volume. As a result, the density decreases. This is why ice will float on top of water; ice has a lower density than the water.

The first thing to be affected by alcohol is Judgement followed by brain center and senses like smell, taste, vision, etc...

A man with colour blindness will see red and green as same. 

Three main enzymes, pepsin secreted by the stomach and trypsin and chymotrypsin secreted by the pancreas, break down food proteins into polypeptides that are then broken down by various exopeptidases and dipeptidases into amino acids.

Hence, digestion of protein begin in stomach.

‘has’ is incorrectly used since the sentence is in past tense. Moreover, the subject is cities, which is plural.