-ity
For 200 points, use the -ity form of 'probable' in a sentence
Probability
For 300 points, use the -ity form of 'acid' in a sentence
Acidity
For 400 points, use the -ity form of 'reliable' in a sentence
reliability
For 500 points, use the -ity form of 'hilarious' in a sentence
Hilarity