Which is the tallest tree?

Which of the following is a bidentate ligand?

The term independent of $x$ in the expansion of $\left(\sqrt{x}-\frac{2}{\sqrt{x}}\right)^{18}$ is

Which of the following gases present in the air darkens the surface painted with white lead?

The straight lines represented by the equation $9x^2 - 12xy + 4y^2 = 0$ are

$AgNO_3 \xrightarrow{\Delta} (W) + (X) + O_2$
$(X) + H_2O \to HNO_2 + HNO_3$
$(W) + HNO_3 \to (Y) + NO + H_2O$
$(Y) + Na_2S_2O_3 (\text{excess}) \to (Z) + NaNO_3$
Identify $(W)$ to $(Z)$.