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Radioactive elements whose nuclei are unstable and atoms of such elements emit alpha-particles or beta-particles along with the gamma-rays. Due to emission of alpha-particles or beta-particles, atomic number and atomic mass are changed. We cannot speed up or slow down this process by any physical or chemical change. It means we cannot affect radioactivity by changing temperature or pressure. Radioactivity is a spontaneous process of nuclear disintegration. Lead is heaviest stableatom. In fact all radioactive elements are finally converted into lead. During a decay,

Answer»

mass number remains unaffected and atomic number INCREASES by 2
mass number increases by 4 and atomic number decreases by 2.
mass number increases by 4 and atomic number decreases by 1.
mass number decreases by 4 and atomic number decreases by 2.

Answer :D


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