http://i68.tinypic.com/alg188.jpg - Question 19 why is the answer (c)..?

19.
A more reactive can displace a less reactive metal from the solution of its salt.
A less reactive cannot displace a more reactive metal.

Nickel can displace P, but cannot displace Q or R. Reactivity: (Q, R) > Ni > P
Iron can displace P and Q, but cannot displace R. Reactivity: R > Fe > (P, Q)
Hence, R > Fe > Q > Ni > P

...... The answer is: C. R, Fe, Q, Ni, P