[" 4) 12.25"],[" Woron has two istopes B's & B't whose 9."],[" relative abudances are "20^(@)/" ."&80^(@)/^(" - ")],[" respectively ave.atomic wieght of Boron is? "],[[" 1) "10," 2) "11],[" 3) "10.5," 4) "10.8]]