Answer:
c. Friction will be in the opposite direction of the block's motion because molecular interactions between the block and the floor will deform the block in the opposite direction of motion.
Explanation:
When a block is put on the floor , there is interaction at molecular level between the molecules of block and floor . This mutual interaction
( attraction ) pulls them together. When the body is pushed forward, the distance between molecules is increased . Due to mutual attraction , block is deformed at the interface in the opposite direction of motion . This strain causes restoring stress which is also called friction . This elastic stress creates force on the block in backward direction and force on the floor in forward direction .