Hydrogenation of naphthalene (P) with excess hydrogen gas stops cleanly at 1, 2, 3, 4-tetrahydronaphthalene (Q). What conclusion can be drawn from his experiment ?

one aromatic ring of P is more reactive than the aromatic ring of Q

reduction of the first C = C of P is faster than reduction of the second or third C = C

the hydrogenation of P is exothermic

one aromatic ring of P is less reactive than the other ring of Q