Sublimation is a change from the solid phase to thephase

solid to gaseous or gaseous to solid

Explanation:

Sublimation is the transition of a substance directly from the solid to the gas state, without passing through the liquid state. sublimation is most often used to describe the process of snow and ice changing into water vapor in the air without first melting into water.

a) 2Ba + O2 → 2BaO

b) 2HCl + Mg → MgCl2 + H2

c) 2HCl + CuO → CuCl2 + H2O

d) Fe + O2 → Fe2O3

Explanation:

Okay so for

a), you must add 2 at the front of Ba and BaO bcuz you're gonna need your equation balanced.

like as you can see, O has 2 so yeahh, you've got to balance it nicely.

b) you must add 2 in front of HCl bcuz the Cl and H after the reaction happened has 2 in them, were talking about balancing so XD

c) and yes again, you're gonna have to add 2 in front of HCl bcuz of the same reason as b).

d) D is definitely a special case bcuz, Fe3+ with O2, so well if you do the cross multiplication technique you'll automatically get Fe2O3. Yas that's it.

English is not my first language so it's hella tuff to explain it to you from in much more detailed perspective T-T Sorry (´∩｡• ᵕ •｡∩`)