Question

The outermost subshell configuration of element A is 3s²3p⁵ and the element B is 3s². What is the chemical formula of the compound formed by A and B ?

1.AB
2.BA₂
3.AB₂​

Answer 1

Answer:

Option 3

Explanation:

ns2 np3 is outer electronic config of halogens

ns2 is outer electronic config of alkaline earth metals

and they form compounds of formula MX2 just like BeCl2

although here the elements are Mg(3s2) and Cl(3s2 3p5)

Answer 2

Answer:

3. $AB_2$ is the right answer.

Explanation:

A has an electronic configuration 3s²3p⁵  which makes it a halogen with a valency of -1

B has an electronic configuration of  3s² which makes it an alkali earth metal with a valency +2

Therefore be can say that the formula of the compound will be $B_2A$ or $AB_2$