The half-life of a sample of a radioactive substance is 1 hour. If \[8\times {{10}^{10}}\] atoms are present at \[t=0\], then the number of atoms decayed in the duration \[t=2\] hour to \[t=4\] hour will be [MP PMT 2004]

• A.            \[2\times {{10}^{10}}\]    
• B.            \[1.5\times {{10}^{10}}\]
• C.            Zero                                          
• D.            Infinity