Question

Two resistors R1 and R2 may form (a) a series combination or (b) a parallel combination and the combination may be connected to a 6 V in which c

Answer 1

I don't know what is your question because the question you posted is incomplete, but anyway I'll try to solve.

Series combination

Re=R1+R2

In this case each resistor has its own value of potential, different from the other resistor. But their sum will be equal to 6V.

Parallel combination

1/Re=1/R1+1/R2

In this case both the resistors will have same value of potential which is 6V.