Which metal oxide is used to make blue glass?

Write about the utility of $d$- and $f$-block elements and their compounds. Or describe the following uses of $d$- and $f$-block elements and their compounds: $(i)$ In iron/steel $(ii)$ As pigments $(iii)$ In batteries $(iv)$ In coinage $(v)$ As catalysts.

When $XO_2$ is fused with an alkali metal hydroxide in the presence of an oxidizing agent such as $KNO_3$,a dark green product is formed which disproportionates in an acidic solution to afford a dark purple solution. $X$ is

Which one of the following is an amphoteric oxide?

In the structure of the dichromate ion,there is a :

Which of the following exhibits the maximum oxidation state of vanadium?