$ \Rightarrow(2 \alpha+3)\left\{\frac{7 \alpha}{6}\right\}-(3 \alpha+1)\left\{\frac{-7}{6}\right\}=0 $
$ \Rightarrow(2 \alpha+3) \cdot \frac{7 \alpha}{6}+(3 \alpha+1) \cdot \frac{7}{6}=0 $
$ \Rightarrow 2 \alpha^2+3 \alpha+3 \alpha+1=0 $
$ \Rightarrow 2 \alpha^2+6 \alpha+1=0 $
$ \Rightarrow \alpha=\frac{-3+\sqrt{7}}{2}, \frac{-3-\sqrt{7}}{2}$
Hence option $(2)$ is correct.