Question

The formula of the compound is ${A_2}{B_5}$ ​. The number of electrons in the outermost orbits of A and B respectively are:
A. 6 and 3
B. 5 and 2
C. 5 and 6
D. 2 and 3

Answer 1

In order to answer this question, you must be aware of the concepts of valency of elements in a compound. Use the formula for finding the valency of the elements in the compound ${A_2}{B_5}$ . Then calculate the number of electrons in the outermost shell of these elements by observing their valencies. Then apply the same formula to make the equation in the correct proportion and then you will get the correct answer.

Complete step-by-step solution: Step 1: In this step, we will enlist the formula which we will use for finding the valencies of A and B:The formula is ${C_1}{N_1}\,\, = \,\,{C_2}{N_2}$ ; where $C$ represents the component and $N$represents its quantity.
Step 2: In this step, we will use the above listed formula to find the answer:
On putting the values in the formula, we get,
$A \times 2\,\, = \,\,B \times 5$
But, clearly the valency of A is 2,
Hence, ${N_1}$ = (8-valency) (ie. ${N_1}$ $= 8 - 2 = 6$)
So, the formula becomes $A \times 6 = B \times 5$ $\Rightarrow \,\,$ $\dfrac{A}{5} = \dfrac{B}{6}$
Therefore, the answer is A=5 and B=6 Where, ${N_1}$ is the no. of valence electrons in A and ${N_2}$ is the no. of valence electrons in B.

Hence, the correct answer is option C.

Note: If the outermost shell of the atom has 8 electrons then the element is said to have a complete octet. By gaining, sharing and losing the electrons the atoms complete their outermost orbital and make an octet. The capacity of an atom can be described by the total number of electrons lost, gained or shared to complete its octet and it also determines the valency of the atom.