Please explain this :

Frequency is given by,
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Frequency is proportional to square root of tension. As the frequency is doubled
$$\begin{gathered} 2f =\frac{1}{2L}\sqrt{\frac{T_2}{\mu }} \\ 2\frac{1}{2L}\sqrt{\frac{T_1}{\mu }} =\frac{1}{2L}\sqrt{\frac{T_2}{\mu }} \\ 2\sqrt{T_1} =\sqrt{T_2} \\ 4T_1 =T_2 \end{gathered}$$
So correct option is A

Regards