Answer:
The algebraic expression which is a polynomial with a degree of 2 is:
4)

Explanation:
Polynomial expression--
It is a algebraic expression which contains the natural powers of x.
We know that the general form of a quadratic polynomial i.e. a polynomial of degree 2 is given by:

where a,b and c are real numbers.
1)

It is a cubic polynomial i.e. a polynomial of degree 2.
Since the highest power of x in the expression is: 3
2)

It is not a polynomial since there is one term which is not a natural power of x.
3)

Again we have a term which is not a natural power of x.
Since,

4)

It is a polynomial with degree 2 since it matches the general form of a polynomial of degree 2.