Yes
The set of positive integers does not contain the additive inverses of all but the identity. It is, therefore, not a group.
no
Any set where the result of the multiplication of any two members of the set is also a member of the set. Well known examples are: the natural numbers (ℕ), the integers (ℤ), the rational numbers (ℚ), the real numbers (ℝ) and the complex numbers (ℂ) - all closed under multiplication.
NO. Certainly not. Additive inverse and Multiplicative inverse doesn't exist for many elements.
No. The set does not include inverses.
No. The inverses do not belong to the group.
The set of integers, under addition.
The set of integers is not closed under multiplication and so is not a field.
Yes!
Yes!
Yes
They are not the same!The set of integers is closed under multiplication but not under division.Multiplication is commutative, division is not.Multiplication is associative, division is not.
No, it is not.
Yes.
Yes.
If you mean the set of non-negative integers ("whole numbers" is a bit ambiguous in this sense), it is closed under addition and multiplication. If you mean "integers", the set is closed under addition, subtraction, multiplication.