(1) In compound A, positive charge on O atom is not stable that is why $$\mathop O\limits^ \oplus {H_2}$$ get's removed.

(2) In Carbocation (B), two $$\alpha$$-H present and after 1, 2-methyl shift number of $$\alpha$$-H becomes six so it becomes more stable as far carbocation when number of $$\alpha$$-H increases stability increases.

(3) Among product D, E and F, D is major product as in case of alkene most stable, alkene are those which have more $$\alpha$$-H. And every reactant produce that product which is more stable.