[" 29.A sample radio active subsistence has "10^(@)" radio "],[" active radio active nuclei.It's half-life is "20" sec.How "],[" many nuclei will remain after "10" seconds? "],[[" 1) "7times10^(5)," 2) "8.5times10^(5)],[" 3) "8times10^(5)," 4) "7.5times10^(5)]]