The law uses the product of the two symbols and the exponent \(\frac{p-1}{2}\cdot\frac{q-1}{2}\). The other choices confuse the law with an equality or with a simple parity formula.
The law of quadratic reciprocity relates the Legendre symbols \(\left(\frac{p}{q}\right)\) and \(\left(\frac{q}{p}\right)\) for distinct odd primes \(p\) and \(q\).