If two angles are linear pair, can they both be acute

No ... a linear pair is a straight line ... two acute angles wouldn't create a straight line

No. A linear pair of angles is a pair that add up to 180 degrees. So their average is 90 degrees each. If they are not both 90-degree (right) angles, then one of them must be bigger than 90 ... an obtuse angle ... while the other one is less than 90 ... an acute angle.