When a manganese $(Mn^{II})$ salt is fused with a mixture of $KNO_3$ and solid $NaOH$,what will be the oxidation state of $Mn$ after it changes from $+2$?

Fill in the blanks:
$(a)$ The unit of magnetic moment is ......... .
$(b)$ $Mn^{2+}$ has .......... color.
$(c)$ $Fe_3H$ is a ............. type of compound.

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.

What are the impurities present in ruby and sapphire?

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

Which compound is formed when iron reacts with carbon?