Under what operations are the set of integers closed? explain your answer.

Addition, subtraction, multiplication.

Addition: The addition of two integers produces another integer.

Subtraction: The subtraction of two integers produces another integer.

Multiplication: The product of two integers is an integer.

Division between two integers can produce a rational number that is not in the set of integers e.g. 1/3

This only includes the four basic arithmetic operations, you can include exponentiation and the modulo operation if you want to for the same reasons as above.