Reasonable means that whatever decision was made is appropriate given the particular circumstances, and most would regard it as so.
Justified means that whatever decision was made is done for a good reason, in the interest of fairness.
There are times the words could be used interchangeably, and contexts where the difference is subtle. It all depends on the nature of the request or issue at hand.
I might use "justified" if I was angry about something, and was acting in response:
Was it polite to skip their wedding after they insulted me like that? No, but I think my decision was justified.
I might use "reasonable" if I think everyone would agree that there was nothing else that could be done:
Was I happy about missing their wedding so that I could go to my mother's funeral? No, but I think my decision was reasonable.
But there are contexts where either word will work just fine:
You said that you'd deliver the cake before noon, but it didn't get here until 3 o'clock. I think my request for a refund is reasonable/justified.
In that sentence, reasonable would work because most people would agree that a refund would be appropriate given the circumstances, and justified would work because the request is fair.
Most of the time, there is no difference. "Some thing" is much much less common than "something", however, so the only reason to write it as two separate words is to emphasize the "some" part (in contrast to "any" or "no" thing):
I want to get her some thing for Valentines Day, but not just anything.
It has to be something she would like.
Another possibility is that the writer uses separate words to emphasize the "thing" part (in contrast to some one). To quote Jim Carrey quoting Shatner from an old "Twilight Zone":
There's someone on the wing! Some ... thing!
Still, it is rare and the example you quote is more likely a typo than intentional.
Best Answer
By1) I love singing.
2) I love to sing.
Love is one of the verbs that takes after it either a to-infinitive or an -ing form, without any difference in meaning.
No doubt, according to grammar, although both sentences should convey the same meaning, the sentence #1 is a bit ambiguous. This ambiguity arises because "singing" is not only a verb (present participle) but also a noun that means an act or performance of singing. So the sentence may also be understood to mean that you love to hear singing or love to hear people sing. However, if there is an object after "singing" such as I love singing songs/this song, there is not an iota of doubt that you love to sing.