Which of the following alloys is used in the construction of the outer fuselage of ultra-high-speed aircraft?

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

Which metal oxide is used to make blue glass?

Which transition element of the $3d$ series is used in a dry battery cell?

$MnO_2$ when fused with $KOH$ and oxidised in air gives a dark green compound $X$. In acidic solution,$X$ undergoes disproportionation to give an intense purple compound $Y$ and $MnO_2$. The compounds $X$ and $Y$,respectively,are

Give the formulas of the oxocations of the $3d$ series metals.