two tenses in a sentence

may i know, can we make a sentence with two tenses…

for example:
" 2% drug was selected for this study as it has the lowest droplet size and PDI index"

Of course: ‘I ate breakfast today and I will eat breakfast tomorrow.’

Yes, you can get a mix of tenses.

In your sentence, the first part is referring to a completed action in the past (so past simple) and the second part to something that is always true (present simple).

Your grammar is wrong though. Do you mean:

2% of the drug was…