(i) is a polynomial of degree 2.i.e Quadratic polynomial.
(ii) is a polynomial of degree 2 in y variable. i.e. Quadratic polynomial.
(iii)
It is not a polynomial because exponent of x is 1/2 which is not a positive integer.
(iv)
It is not a polynomial because is fractional part.
(v)
It is a polynomial in three variables x, y and t.