Calculate the percent activity of the radioactive isotope iridium-192 remaining after 2 half-lives.

The percentage activity of radioactive  isotope iridium 192 remaining is  25%  after  2  half    lives.The duration  of two  half-  lives  means  that  iridium-192 undergo decay for  two  times,  that  is
After one  half  live 50%  remains
After  two  half live  25%remains 

The reaction 2kalsi3o8 + 2(h+ + hco3-) + h2o  →  al2si2o5(oh)4 + 2k+ + 2hco3- + 4sio2 shows that feldspar kalsi3o8 is chemically altered by hydrolysis to form chalky-looking clay mineral kaolinite al2si2o5(oh)4. the chemical breakdown of potassium feldspar due to exposure to acidic water results to the mineral binding with the water molecule to become kaolinite with silica and potassium and bicarbonate ions in solution.