Question

in f2 generation why did Mendel use 2 pea plants instead of one as both are tall he could have taken any one tall pea plant right?

Answer 1

reproduction can only occur taking two One female and one male.

Because two gametes are required for a sexual reproduction. Each allele from each parent is obtained by the offspring.

Even in punnette square one can observe that one allele is taken from one parent and other from another parent.

For any further doubts you are free to ask me ☺

Hope it helps