Three term cards P, Q and R are shown. Which statement about them is true?

Literal coefficients: P has $m{n}^2$, Q has $m{n}^2$, R has $m^{2}n$, so only P and Q match. Q is $1\cdot m{n}^2$, so its numerical coefficient is 1, not 0; P has $-8$ and R has $8$, which differ.