In a nuclear reactor, material used for control rods is,

The compound that is used in nuclear reactors as protective shields and control rods is

Consider the following statements : 1. The chain reaction process is used in nuclear bombs to release a vast amount of energy, but in nuclear reactors, there is no chain reaction. 2. In a nuclear reactor, the reaction is controlled, while in nuclear bombs, the reaction is uncontrolled. 3. In a nuclear reactor, all operating reactors are 'critical', while there is no question of 'criticality' in case of a nuclear bomb. 4. Nuclear reactors do not use moderators, while nuclear bombs use them. Which of the above statements about operational principles of a nuclear reactor and a nuclear bomb is/are correct?