A student performed the first set of experiments with four test tubes containing solutions and metal pieces as indicated in the figure. In the second set of experiments, the metal pieces are interchanged between test tubes P and Q and also between test tubes R and S.

In which test tube(s), no reaction will occur in both sets of experiments ?

Options

A. P and Q
B. R
C. S
D. R and S

Answer

B

Explanation

In the first set of experiments,
P: No reaction occurs as Cu is less reactive than Zn.
Q: Reaction occurs as Mg is more reactive than Fe.
R: No reaction takes place as Zn is less reactive than Mg.
S: Reaction occurs as Fe is more reactive than Cu.
In the second set of experiments,
P: Cu is replace by Mg. the reaction occurs as Mg is more reactivie than Zn.
Q: Mg is replaced by Cu. the reaction does not occur as Cu is less reactive than Fe.
R: Zn is replaced by Fe. No reaction occurs as Fe is less reactive than Mg.
S: Fe is replaced by Zn. the reaction occurs as Zn is more reactive than Cu.
Therefore, in test tube R, no reaction will occur in both sets of experiments.