http://i68.tinypic.com/9j0ku0.jpg - question 25 why is the answer (b)..?

25.
A more reactive metal can displace a less reactive metal from its salt.
However, a less reactive metal cannot displace a more reactive metal.

When nickel (Ni) is put into the three solutions, nickel can displace P, but cannot displace Q and R. This means that nickel is more reactive than P but less reactive than Q and R.
Reactivity : (Q, R) > Ni > P ...... [1]

When iron (Fe) is put into the three solutions, iron can displace P and Q, but cannot displace R. This means that iron is more reactive than P and Q, but less reactive than R.
Reactivity : R > Fe > (P, Q) ...... [2]

Combining [1] and [2], the reactivity : R > Fe > Q > Ni > P

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

.