Question

How can 3 resistors of 2,3,6 ohm connected in circuit to give a total resistance of 1 ohm

Answer 1

if they connected in parallel connection than the total resistance can be 1 ohm

1/r=1/2+1/3+1/6
taking l.c.m
1/r=3+2+1/6
1/r=6/6

therefore r=1 ohm

Answer 2

if you put all the 3 resistors in parallel then

1/2 + 1/3 + 1/6 = (3+2+1)/6
=6/6= 1 ohm