Rishita studied the reactions of some metals with dilute hydrochloric acid

in her school lab under the supervision of her teacher. She summarised her

observations as                      

I) When metal P was added to acid, the reaction was slow in the beginning

and rapid after some time.

II) When metal Q was added to the acid, only a few gas bubbles were

formed.

III) No change was observed when metal R was added to the acid.

IV) Explosive reaction occurred when metal S was added to the acid.

Metals P, Q, R, and S could be respectively.