Fill in the blanks:
$1.$ Heating lanthanoids with sulfur gives .......
$2.$ Mixed oxides of lanthanoids are used as catalysts in ..........

Among the following oxides of $3d$ elements, the number of mixed oxides are . . . . . .
$Ti_{2}O_{3}, V_{2}O_{4}, Cr_{2}O_{3}, Mn_{3}O_{4}, Fe_{3}O_{4}, Fe_{2}O_{3}, Co_{3}O_{4}$

Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with $(i)$ iron $(II)$ ions,$(ii)$ $SO_2$,and $(iii)$ oxalic acid? Write the ionic equations for the reactions.

What are the oxidation states of iron in the minerals hematite and magnetite?

Which of the following statements regarding copper salts is not true?

Which lanthanoid compound is used in pigments?