Answer: (3) different decay modes and different half-lives
Explanation: Potassium-37 and Potassium-42 have the same number of protons but different numbers of neutrons i.e. they have same atomic number but different mass number. They are isotopes. Thus K-37 and K-42 have different decay modes
K-37 is positron decay and K-42 is beta decay.
K-37 has a half life of 1.23 seconds and K-42 has a half life of 12.4 hrs.
Thus they have different decay modes and different half lives.
During a beta decay, one neutron convert into one proton and one electron. The proton remained in nucleus while electron move away known as beta radiation. So atomic mass will be remained same but atomic no will increase by one. So correct ans will be with 218, 86 Po and beta radiation.