Question

12 Element X is in Period 3. Element X forms a solid oxide Y. Y reacts with hot concentrated hydrochloric acid. Y reacts with hot aqueous sodium hydroxide to form a compound in which X is part of an anion. How many p electrons does one atom of X have in its outer shell? Α Ο B 1 C 2 D 3​

Answer 1

The correct option is D.

• The period 3 elements are Na,Mg,Al,Si,P etc.
• Si and P on reaction with oxygen form solid oxides. So, X can be Si or P.
• The oxides are $SiO_2,P_2O_5$. So, Y can be $SiO_2,P_2O_5$.
• Now Y reacts with hot concentrated hydrochloric acid. But silicon dioxide does not react with HCl. So, Y is phosphorus pentoxide.
• Now Y reacts with hot aqueous sodium hydroxide to form a compound in which X is part of an anion. The reaction between phosphorus pentoxide and NaOH is-

$P_2O_5+6NaOH\rightarrow 2Na_3PO_4+3H_2O$

• In $Na_3PO_4$ P is present in $PO_4^{3-}$.
• So, X is P and its electronic configuration is
• $1 {s}^{2} 2 {s}^{2}2 {p}^{6} 3 {s}^{2} 3 {p}^{3}$
• So, p orbital contains 3 electrons.