The electronic configuration of two elements A and B are given below, the molecular formula of compound formed from A and B will be :
$A=1s^{2},2s^{2},2p^{6},3s^{2},3p^{3}$
$B=1s^{2},2s^{2},2p^{6},3s^{2},3p^{5}$

Question

The electronic configuration of two elements A and B are given below, the molecular formula of compound formed from A and B will be : 
$A=1s^{2},2s^{2},2p^{6},3s^{2},3p^{3}$ 
$B=1s^{2},2s^{2},2p^{6},3s^{2},3p^{5}$

Accepted Answer

To determine the molecular formula of the compound formed from elements A and B, we need to analyze their electronic configurations and deduce their valencies.

1. **Element A**: The electronic configuration of A is $1s^{2}, 2s^{2}, 2p^{6}, 3s^{2}, 3p^{3}$. This configuration indicates that element A is in the third period and belongs to Group 15 of the periodic table, which is the nitrogen group. Elements in this group typically have five valence electrons (3s²3p³) and require three more electrons to achieve a stable octet configuration. Therefore, the valency of A is 3.

2. **Element B**: The electronic configuration of B is $1s^{2}, 2s^{2}, 2p^{6}, 3s^{2}, 3p^{5}$. This configuration shows that element B is in the third period and belongs to Group 17 of the periodic table, which is the halogen group. Elements in this group typically have seven valence electrons (3s²3p⁵) and need one more electron to complete their octet. Thus, the valency of B is 1.

Given these valencies, we can determine the molecular formula of the compound formed by A and B:

- Element A, with a valency of 3, will need three atoms of element B, each with a valency of 1, to satisfy its valency requirement. This leads to the formation of a compound with the formula $AB_{3}$.

**Explanation of Options**:

1. **Option 1: AB** - This option suggests a 1:1 ratio between A and B. However, since A has a valency of 3 and B has a valency of 1, a 1:1 ratio would not satisfy the valency requirements of A.

2. **Option 2: $A_{2}B$** - This option suggests a 2:1 ratio, which would imply that two atoms of A combine with one atom of B. This does not satisfy the valency requirements because each A atom needs three B atoms to achieve a stable configuration.

3. **Option 3: $AB_{2}$** - This option suggests a 1:2 ratio, which would imply that one atom of A combines with two atoms of B. This does not satisfy the valency requirements because A needs three B atoms to complete its octet.

4. **Option 4: $AB_{3}$** - This option correctly represents the 1:3 ratio needed to satisfy the valency requirements of both elements. One atom of A combines with three atoms of B, allowing A to achieve a stable octet configuration.

Therefore, the correct molecular formula of the compound formed from elements A and B is $AB_{3}$, making Option 4 the correct answer.