Number of molecules/ions from the following in which the central atom is involved in \( \mathrm{sp}^3 \) hybridization is \( \_\_\_\_\_\_ \).\( \mathrm{NO}_3^- , \ \mathrm{BCl}_3 , \ \mathrm{ClO}_2^- , \ \mathrm{ClO}_3 \)
\( 4 \)
\( 3 \)
\( 2 \)
\( 1 \)