Is zero a rational number

Zero is a rational number. It can be written as a ratio: 0/1, 0/2, etc.

From MathsIsFun, here is a formal definition (I copied and pasted, OK)

A rational number is a number that can be in the form p/q where p and q are integers and q is not equal to zero.

Besides, for the set of rational numbers to be closed for addition and subtraction, it is necessary for zero to be a rational number. Example: If you say that you can add any two rational numbers and get another rational number, then what happens if you add 1/2 and -1/2, you get zero, so zero would need to also be a rational number.
Yes because it can be expressed as a quotient of two integers. (i.e. 0/1 or 0/2 etc.)