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

Acidified potassium permanganate solution oxidises oxalic acid. The spin-only magnetic moment of the manganese product formed from the above reaction is $.... \, B.M.$ (Nearest Integer)

Which of the following is amphoteric?

Indicate the steps in the preparation of:
$(i)$ $K_2Cr_2O_7$ from chromite ore.
$(ii)$ $KMnO_4$ from pyrolusite ore.

Which of the following statements is true for $Fe_3O_4$?

Which one of the following species is stable in aqueous solution?