Questions

Sum of all numbers in each row and columns must be 15.

In last row to gt sum as 15 missing number must replaced by 1. 

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

Fractional distillation is the process of seperation of a mixture of two or more liquids into the different fractions, which differ fairly widely in their boiling points. The liquid with a lower boiling point will be vaporized first and hence would be the distillate (first fraction). Eg. Ethyl alcohol has a boiling point of 78.10C and water 1000C. When a mixture of these two liquids is heated, alcohol vaporizes first and is collected separately as the distillate. 

Water is the important nutrient all organisms need. Humans has almost 60% of their body weight is water. Some organisms have 90% of their body weight is of water.