Book started to loose contact with shelf when maximum acceleration $a$ of shelf is such that,
$a_{\max } \geq g$
$\Rightarrow \quad \omega^2 A \geq g$
$\Rightarrow \quad \omega^2=\frac{g}{A}$.
So, frequency of oscillations is
$f=\frac{\omega}{2 \pi}=\frac{1}{2 \pi} \sqrt{\frac{g}{A}}$
$\Rightarrow \quad f=\frac{1}{2 \pi} \cdot \sqrt{2.5 \times 10^{-2}}=\frac{2 \times 10}{2 \pi}$
$\Rightarrow \quad f \approx 3.18 \,Hz$
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${C_6}{H_5}CHO + C{H_3} - CHO\xrightarrow{{\mathop O\limits^\Theta H}}$ Product
will be
$C{{H}_{3}}-C\equiv CH\xrightarrow[{{H}_{2}}S{{O}_{4}}]{HgS{{O}_{4}}}A\xrightarrow{NaB{{H}_{4}}}B$
