Two blocks A and B of masses 5 kg and 2 kg, respectively, connected by a spring of force constant = 100 N m^-1 are placed on an inclined plane of inclination ${30}^{\circ }$ as shown in figure. If the system is released from rest

There will be elongation in the spring if A is smooth and B is rough.

There will be no compression or elongation in the spring if all surfaces are smooth.

There will be elongation in the spring if A is rough and B is smooth.

Maximum elongation in the spring 35 cm if all surfaces are smooth.