$$A + 2B \rightarrow AB_{2}$$
36.0 g of ' A' (Molar mass : 60 g $$mol^{-1}$$) and 56.0 g of 'B' (Molar mass: 80 g $$mol^{-1}$$) are allowed to react. Which of the following statements are correct?
A. 'A' is the limiting reagent.
B. 77.0 g of $$AB_{2}$$ is formed.
C. Molar mass of $$AB_{2} is 140 g $$mol^{-1}$$
D. 15.0 g of A is left unreacted after the completion of reaction.
Choose the correct answer from the options given below :

We need to identify correct statements about the reaction $$A + 2B \rightarrow AB_2$$. Since 36.0 g of A (M = 60 g/mol) and 56.0 g of B (M = 80 g/mol) are provided, we first calculate the amount of each reactant in moles: Moles of A = $$36/60 = 0.6$$ mol and moles of B = $$56/80 = 0.7$$ mol.

Because the stoichiometry requires 2 moles of B per mole of A, the 0.6 mol of A would consume $$0.6 \times 2 = 1.2$$ mol of B, but only 0.7 mol is available. Therefore B is the limiting reagent, which means Statement A that claims A is limiting is incorrect.

In this context, 0.7 mol of B reacts completely with $$0.7/2 = 0.35$$ mol of A to produce 0.35 mol of $$AB_2$$. The unreacted A amounts to $$0.6 - 0.35 = 0.25$$ mol, corresponding to $$0.25 \times 60 = 15.0$$ g, so Statement D is correct.

The molar mass of $$AB_2$$ is $$60 + 2(80) = 220$$ g/mol, so Statement C, which suggests 140 g/mol, is incorrect. The mass of $$AB_2$$ formed is $$0.35 \times 220 = 77.0$$ g, confirming that Statement B is correct.

The correct answer is Option 3: B and D only.