number of neutrons
Step 1: Isobars are atoms (not necessarily of the same element) that have the same mass number but different atomic numbers.
Step 2: The mass number is defined as the total number of protons and neutrons in an atom's nucleus.
Step 3: Isobars have the same total number of nucleons (protons plus neutrons), which results in the same mass number.
Step 4: Therefore, the defining characteristic of isobars is that they share the same mass number, aligning with option (B).
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 :