The logic circuit shown in figure yield the following truth table. What is the gate X in the diagram ?

From the truth table we note thatY = A + BBut Y=A+X=A+B=A+B . (A+A¯)=A+B⋅A+B⋅A¯=A(1+B) + B⋅A¯=A+A¯B⇒X=A¯B which is AND gate with input as A¯ and B so gate X is AND gate