Question

Two elements X and Y contain only one electron in the outer level.Element X is reactive and loses electron easily while element Y is relatively unreactive and non corrosive. The elements X and Y respectively are

(a)Cs and Cu

(b)Li and Cu

Answer 1

From the options, we can understand the Y is Cu also we know that Cu is non corrossive and relatively unreactive

Now,we have to find X

That is ,Li or Cs which is more reactive and easily lose electrons

Lithium (li) and Cesium (cs) both are come under active metal.

But Cesium is more active, they both have the same amount of valence electrons, but Cesium is a larger atomic nucleus with a larger charge of positive particles (protons) than its related compound lithium.

As nucleus of an atom grows larger (as in the case of Cesium vs. Lithium), the electrons go into shells that are further away to distribute the energy of said nucleus. Therefore, the electrons of Cesium are much more further away (to stabilize the charge of the nuclear center) and thus are much easier to force into a chemical reaction than lets say, lithium. Lithium has its electrons pulled closer to the positive charged nucleus (because they are physically closer to the atom) and thus is less reactive than Cesium.

So answer is
option A
X is CS
Y is Cu