Which complex absorbs the wavelength of red light?

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 $Cl = 35.5 \ amu$]

How does ammonia react with a solution of $Cu^{2+}$?

In which one of the following pairs of ions is there an ion that forms a coordination compound with both aqueous sodium hydroxide and ammonia,and another ion that forms a coordination compound only with aqueous sodium hydroxide?

Which of the following is a spin-free complex?

What is meant by stability of a coordination compound in solution? State the factors which govern stability of complexes.