Questions

Convex mirror is used as rear view mirror in vehicles. Because the image is smaller, more image can fit onto the mirror, so a convex mirror provides for a larger field of view than a plane mirror. This is why they are useful.

A candidate key is a column, or set of columns, in a table that can uniquely identify any database record without referring to any other data. Each table may have one or more candidate keys, but one candidate key is unique, and it is called the primary key.

All proteins, carbohydrates and fats are macronutrients that we need to make living. They contribute to 90% of the dry weight of our diet. 

From the given options, Excess carbohydrates and fats are stored; excess proteins are not.

Chemical weathering is the process of altering rocks chemically when they are broken down. It includes hydrolysis, oxidation, acid rain, etc...