Why is `HNO_2` not stable.

Why is +2 oxidation state of manganese quite stable, while the same is not true for iron ?

Why is + 2 oxidation state of manganese (Z=25) more stable than its + 3 oxidation state ?

Why is + 4 oxidation state of titanium more stable than its +3 state? (Z = 22)

Which is most stable ecosystem?

A given nitrogen-containing aromatic compound ‘A’ reacts with Sn/HCl, followed by HNO_2 to give an unstable compound '‘B'. 'B', on treatment with phenol, forms a beautiful coloured compound 'C' with the molecular formula C_12H_10N_2O . The structure of compound 'A' is

Which of the following complexes formed by Cu^(2+) ions is most stable ?

The most stable ion is