Answer is:Ā sp3 on nitrogen overlaps with 1s on hydrogen.
Electron
configuration for nitrogen: āN
1s² 2s² 2p³.
Electron
configuration for hydrogen: āHĀ 1s¹.
The central atom in ammonia, nitrogen, isĀ sp3Ā hybridized (oneĀ sĀ and threeĀ p-orbitalsĀ will combine for a four sp3Ā hybridized orbitals), because sp3 orbitals have lower energy.