\(250\mathrm{mL}\) of \(0.5\mathrm{M}\mathrm{NaOH}\) was added to \(500\mathrm{mL}\) of 1 M HCl. The number of unreacted…

\(250\mathrm{mL}\) of \(0.5\mathrm{M}\mathrm{NaOH}\) was added to \(500\mathrm{mL}\) of 1 M HCl. The number of unreacted \(\mathrm{HCl}\) molecules in the solution after complete reaction is ___________\(\times {10}^{21}\) (Nearest integer) \(\left({\mathrm{N}}_{\mathrm{A}}=6.023\times {10}^{23}\right)\)

[JEE Main 2021, 20 Jul (Shift 1)]