Q

The wire CD is not free to move, while AB is free to move.

 

When the current is flowing through CD, it produces a magnetic field around it.

 

According to right-hand thumb rule, the direction of this field on wire AB will be into the page.

 

Now, in the presence of this external field, the current carrying wire AB will experience a force.

The direction of this force will be given by Fleming's left hand rule.

 

If we place the index finger in the direction of field (into the page) and the middle finger in the direction of current (towards right),

then the thumb points in the upward direction (force). Hence, the wire AB will move upwards.