Resonance occurs in a series $L-C-R$ circuit when the frequency of the applied emf is $1000 Hz$. Then :

At resonance $X_L=X_C$ and $Z=Z_{min}=R$

$X_L=\omega L$ and $\frac{1}{\omega C}=X_C$

If ‘$f$ ’ is decreased then ‘$\omega$’ will decrease and hence $X_C$ will increase therefore at $f<f_r$, circuit behaves as capacitive.
$V_L$ and $V_C$ always difference in phase by $180°$ at any frequency.

If C" = 2C , $\omega "=\frac{\omega }{\sqrt{2}}=\frac{1000}{\sqrt{2}}Hz$