Step 1: Grasp beta decay. Beta decay involves a neutron transforming into a proton, releasing an electron (beta particle) and an electron antineutrino.
Conclusion: Beta decay is the accurate nuclear process, matching option (3).
A small bob A of mass m is attached to a massless rigid rod of length 1 m pivoted at point P and kept at an angle of 60° with vertical. At 1 m below P, bob B is kept on a smooth surface. If bob B just manages to complete the circular path of radius R after being hit elastically by A, then radius R is_______ m :