Abhinav, a class 9 student arranged the given experimental set-up to study the reactivity of some metals with water.
He summarised his observations as follows:
I. In test tube P, there was no reaction in cold water but when the test tube was heated for a while, bubbles of gas were seen.
II. In test tube Q, bubbles of gas were formed only after boiling the water.
III. In test tube R, no gas was produced even on boiling the water.
IV. In test tube S, reaction occurred vigorously.
The metals present in test tubes P, Q, R and S could be respectively
