Questions

Primary key helps us to identify a row uniquely in a relation

We know that polar substances are soluble in polar solvents and non polar substances are soluble in non-polar solvents only. Here the hydrocarbons are non-polar molecular substances and water is a polar solvent. So water can't dissolve hydrocabons.

Hence, as hydrocarbons are non-polar substances, they are insoluble in water as it is a highly polar solvent. 

Here the Nitrogenous Food is Proteins.

Nitrogenous Food ::

The animal body is more than a machine. It requires fuel to enable it not only to work but also to live, even without working. A part of the food eaten must go to maintain the body

Nitrogenous food compounds are sometimes classed together under the name of proteins. These may be divided into proteids, gelatinoids, and extractives.