Which from the following alloys is used in gas turbine engines?

The amphoteric oxide of Vanadium $(V)$ is $V_2O_5$. It reacts with alkali to form an oxoion '$X$' and with acid to form an oxoion '$Y$'. The oxidation states of '$V$' in '$X$' and '$Y$' are respectively:

Which of the following compounds shows colour due to $d-d$ transition?

An aqueous solution of $FeSO_4$,$Al_2(SO_4)_3$ and chrome alum is heated with excess of $Na_2O_2$ and filtered. The materials obtained are

When $MnO_2$ is fused with solid $KOH$ in the presence of air,what is the product formed and its color?

In the reaction $4K_2Cr_2O_7 \xrightarrow{\text{heat}} 4K_2CrO_4 + 3O_2 + X$,the species $X$ is: