Question

If Q reacts with fluorine and oxygen the molecular formula of fluorides and oxide will be respectively: (Q is single electropositive element)
(a)- $Q{{F}_{3}},{{Q}_{2}}{{O}_{3}}$
(b)- $QF,{{Q}_{2}}O$
(c)- $Q{{F}_{2}},QO$
(d)- None of these

Answer 1

Hint: To find the molecular formula of the compounds we have to know the nature of the elements, i.e., the number of valence electrons. We know the valence electron in fluorine is 7 and it requires only 1 more to complete its octet, and oxygen has 6 valence electrons in its valence shell and it requires only 2 to complete its octet. Also given the Q is a single electropositive element, means there is one valence electron.

Complete step by step solution:
As stated above, To find the molecular formula of the compounds we have to know the nature of the elements, i.e., the number of valence electrons.
We are given that element Q is a single electropositive element, which means that it forms a single positive cation, therefore, it has one electron in its valence shell. We know the valence electron in fluorine is 7 and it requires only 1 more to complete its octet. So, to form a compound between Q and F, the fluorine atom will take one electron from Q and the Q will donate one electron and a stable compound will be formed whose formula will be QF.
Oxygen has 6 valence electrons in its valence shell and it requires only 2 to complete its octet and Q has one valence electron. So, two atoms of Q will react with Oxygen to form the stable compound. Therefore, the formula will be ${{Q}_{2}}O$.

Therefore, the correct answer is an option (b).

Note: We know that the Q is a single electropositive element, which means it resembles the alkali metals in the periodic table, so it will be placed in group 1. A stable compound will be formed when all the valances are complete.