Is it correct to say " it will be helpful of yours, if you pass me a pen". If not! then what should be the correct sentence.
2) can we use "plenty of" with count nouns. What other modifiers we can use both with count and uncount nouns.
It would be helpful if you could pass me a pen.
"plenty of" works for both count and non-count nouns. For example,
There is plenty of milk left, and there are plenty of cookies left, too.
Note, the verb agrees in number with the noun (is . . . milk; are . . . cookies)
All the best,