The colour imparted by $Co(II)$ compounds to glass is

In which compound does chromium have a $+6$ oxidation state?

The spin only magnetic moment $(\mu)$ value $(B.M.)$ of the compound with strongest oxidising power among $Mn_2O_3$,$TiO$,and $VO$ is $....$ $B.M.$ (Nearest integer).

Which of the following statements is true for $Fe_3O_4$?

Which of the following statements is true regarding the structure of $Cr_2O_7^{2-}$?

$A$ metal $M$ which is not affected by strong acids like conc. $HNO_3$,conc. $H_2SO_4$ and conc. solutions of alkalies like $NaOH$,$KOH$ forms $MCl_3$,which finds use for toning in photography. The metal $M$ is: