Answer:
14. (a) Pb
15. (d) Al
16. (A) increases
Explanation:
14.
In the reactivity series of metals an element can displace another element from a compound if and only if it is not placed below that metal, as the reactivity of metals decreases when moving from top to bottom- if a metal is placed below Hydrogen it means that it is less reactive than Hydrogen and hence cannot displace Hydrogen from its compound.
All options except A are placed below Hydrogen in the reactivity series, so they wont displace Hydrogen from its compound, but option (a) that is Pb can do so as it is above Hydrogen in the reactivity series.
15.
Al is placed below Mg in the reactivity series and hence cannot displace Mg from its compound.
16.
The reactivity of metals increases down the GROUP.
[CAUTION :- We were talking 'bout REACTIVITY SERIES in the top 2 questions where reactivity decreases down the group, but we're talkin' 'bout GROUPS of the periodic table here, where reactivity increases down the group.]
The size of metals increases down the group causing their valence electrons to drift far from the nucleus so that they can be lost easily. The metals have a property of losing electrons so the more electrons it can lose more will be its reactivity.
Hence, reactivity increases down the group.