Terminal alkyne being thermodynamically less stable than an internal alkyne, instead when 2,2-dibromo butane is treated with NaNH₂, 1-butyne is formed as major product, not 2-butyne because.

terminal bromo alkene is formed in first step of elimination reaction

terminal alkyne forms salt with NaNH₂, phased out of equilibrium

NaNH₂ abstract H from less hindered carbon

NaNH₂ is a very strong base