Question

Which of the following is most stable
A.HF
B.HI
C.HCl
D.HBr

Answer 1

The compounds given above are hydrogen halides. The question is related to stability. Here, stability is something that is related to electronegativity which is indirectly the charge of an atom and also the size. Compare these parameters and observe how they increase or decrease while moving down the group. The stability is also related to how easily an atom can gain or lose electrons.

Complete answer:
I have told you the parameters affecting the stability of an ion. Let us see how these could affect stability. We will start with atomic size, down the group atomic size increases and fluorine is said to be the smallest. When coming to electronegativity, which is the ability of an atom to attract the electrons to form a bond ,the groups. This is because of the fact that as you move down the group atomic size increases because the electrons are added to new energy shells. As the distance increases, the ability to attract the electrons decreases and therefore electronegativity decreases with fluorine being more electronegative. Atoms with more electronegativity hold the electrons more tightly and are more stable. By the above explanation, fluorine being the smallest and most electronegative element,it is said to be more stable. Hence,the order is HF > HCl >HBr >HI.
The correct option is A.

Note:
Any atom is said to be stable based on whether it gains or loses the electrons. This gaining or losing happens mainly to fill the outermost shell and to make it more stable by attaining octet configuration and this is the reason why atoms form ions. More stability, less is the ability to react and vice versa. The stability concept was explained by Rutherford by his atomic model.