<prompt> Least penetrating power -X-rayBeta-raysAlpha particley-rays  <response>: Ans. is c i.e., Alpha particle Penetration power : Gamma rays X rays Beta particle Alpha particle or helium ionIonizing damaging power : is reserve Alpha particle or helium ion Beta particle X ray Gamma rayImportant facts about ionizing radiationso Alpha particles Helium nuclei have highest ionizing power because they have a large charge, o Alpha particles have the highest damaging power as they are relatively slow and heavy,o Gamma rays have highest penetrating power because they are high energy photons.o X-rays have 2nd highest slightly less than g-rays penetrating power,o Gamma rays have minimum ionizing power,o Gamma rays have least damaging power.o Order of penetrating power - Gamma rays X-rays b-particles a-particles.o Order of ionizing damaging power - a-particles b-particles X-rays Gamma rays. 