Which of the following ores is used for the production of $K_2Cr_2O_7$?

Which of the following is used in the manufacture of high refractive index optical glass for cameras?

The first transition series metal $M$ has the highest enthalpy of atomisation in its series. One of its aquated ion $(M^{n+})$ exists in green colour. The nature of the oxide formed by the above $M^{n+}$ ion is $:$

$NaCl$ reacts with conc. $H_2SO_4$ and $K_2Cr_2O_7$ to give reddish fumes $(B)$,which react with $NaOH$ to give yellow solution $(C)$. $(B)$ and $(C)$ respectively are:

Mark the correct statements.

$A$ 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: