The half-life of a radioactive substance against a-decay is \[1.2\times {{10}^{7}}s\]. What is the decay rate for \[4\times {{10}^{15}}\] atoms of the substance [AMU (Med.) 2002]

• A.            \[4.6\times {{10}^{12}}atoms/s\]                                   
• B.            \[2.3\times {{10}^{11}}atoms/s\]
• C.            \[4.6\times {{10}^{10}}atoms/s\]                                   
• D.            \[2.3\times {{10}^{8}}\]