The tendency to form complexes increases with ..........

Complex $A$ has a composition of $H_{12}O_{6}Cl_{3}Cr$. If the complex on treatment with conc. $H_{2}SO_{4}$ loses $13.5\%$ of its original mass,the correct molecular formula of $A$ is :
[Given : atomic mass of $Cr = 52 \ amu$ and $Cl = 35.5 \ amu$]

Which of the following ligands does not act as a $\pi$-acid ligand?

Which of the following molecules is colourless?

Which of the following species exhibits both $LMCT$ and paramagnetism?

In which of the following complexes is the radius of $Fe$ the largest?