(i) Write the type of magnetism observed when the magnetic moments are oppositively aligned and cancel out each other.

(ii) Which stoichiometric defect does not change the density of the crystal ?

(i) In anti-ferromagnetism, the magnetic moments of the atoms, which are the spin of the electrons, where these moments align in opposite directions and so they cancel each other.

(ii) In Frenkel defect, the density of the crystal is not changed. It is a type of stoichiometric point defect in which one of the cations gets misplaced from lattice points and is placed in the interstitial site of the crystal.

Since, there is no loss or gain of any ion, there is no change in its density. Frenkel defect is usually exhibited by crystals such as AgBr, AgCl, AgI, ZnS etc.

Frenkel defect.