Solution:
Solution
$$Let\,\,{\lambda _A} = \lambda ,{\lambda _B} = 2\lambda $$
If No is the total number of atoms in A and B at $$t=0$$; then the initial rate of
disintegration of $$A= \lambda No;$$ and initial rate of disintegration of $$B=2 \lambda No$$
$$\begin{array}{l} As\, \, { \lambda _{ B } }=2{ \lambda _{ A } } \\ { T_{ B } }=\dfrac { 1 }{ 2 } { T_{ A } } \\ { \left( { -\dfrac { { dN } }{ { dt } } } \right) _{ A } }-\dfrac { { \lambda No } }{ 2 } \\ { \left( { -\dfrac { { dN } }{ { dt } } } \right) _{ B } }=2\dfrac { { 2\lambda No } }{ 4 } =\dfrac { { \lambda No } }{ 2 } \\ \therefore n=1,\, \, i.e.,\, \, one\, \, half\, \, life\, \, of\, \, A \end{array}$$