Final answer:
The expressions 3+1/n and q₁/2+5 are not polynomials because they contain, respectively, a variable in the denominator and a fractional exponent.
Step-by-step explanation:
Among the expressions provided, -4p+7 and x² y are polynomials because they consist of a sum of monomials where each variable has a non-negative integer exponent. However, the expressions 3+1/n and q₁/2+5 are not polynomials as they contain a variable in the denominator and a fractional exponent, respectively, which are not allowed in polynomial expressions.