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The reason why bond angle is larger in ${\mathrm{N}\mathrm{H}}_3$ than  ${\mathrm{P}\mathrm{H}}_3$ are given below.

• In ${\mathrm{N}\mathrm{H}}_3$ , there is one lone pair on the nitrogen atom increases repulsion, while the lone pair on phosphorus is in a higher energy orbital and causes less repulsion.
• Nitrogen is a small and electronegative atom whereas phosphorus is larg

The NO (Nitric Oxide) has 11 valence electrons while the NO? (Nitrosonium ion) has 10 valence electrons due to removal of one antibonding electron. Due to this, the bond order of NO increases from? 2.5 to 3 in the NO? (Nitrosonium ion). 

As per the NCERT, since the bond order of NO? (3) is high