situation vs size of it

situation and size of it both are nouns.

Word	Noun	Adjective	Verb	Adverb
situation	Yes	No	No	No
size of it	Yes	No	No	No

As nouns, size of it is a hyponym of situation; that is, size of it is a word with a more specific, narrower meaning than situation:

situation: the general state of things; the combination of circumstances at a given time
size of it: the actual state of affairs

situation (noun)	size of it (noun)
a job in an organization	the actual state of affairs
physical position in relation to the surroundings
the general state of things; the combination of circumstances at a given time
a condition or position in which you find yourself
a complex or critical or unusual difficulty