1.
is not a polynomial, because the degree of second term is negative (-1);
2.
is a polynomial of 4th degree (the highest degree of all terms is 3+1=4);
3.
is a polynomial of 2th degree (the highest degree of all terms is 2);
4.
is not a polynomial, because the degree of second term is a fraction
;
5.
is a monomial with 1st degree;
6.
is not a polynomial, because here the variable x is placed in degree.