Correct Answer - A
As water is considered to be incompressible, so volume covered by inward movement of smaller piston =volume covered by outward movement of larger pistio.
`L_(1)A_(1)=L_(2)A_(2)`
`L_(2)=(A_(1))/(A_(2))L_(1)=(pi(D_(1)//2)^(2))/(pi(D_(2)//2)^(2))L_(1)=((D_(1))/(D_(2)))^(2)L_(1)`
`=((1cm)/(3 cm))^(2)xx 6 cm=(6)/(9) cm=(2)/(3)` cm
