When alcohol vapor is passed over heated reduced copper $(Cu)$,the alcohol is converted into an alkene. Which type of alcohol is this?

The molar enthalpies of combustion of $C_2H_{2(g)}$,$C_{(graphite)}$,and $H_{2(g)}$ are $-1300$,$-394$,and $-286 \ kJ \ mol^{-1}$,respectively. The standard enthalpy of formation of $C_2H_{2(g)}$ is ....... $kJ \ mol^{-1}$.

$\frac{\tan 80^{\circ}-\tan 10^{\circ}}{\tan 70^{\circ}}$ is equal to

In $YDSE$, the separation between the slits is halved and the distance between the slit and the screen is doubled. The fringe width is

The pair of compounds which cannot exist together in aqueous solution is
$I$. $NaH_2PO_4$ and $NaHCO_3$
$II$. $Na_2CO_3$ and $NaHCO_3$
$III$. $NaOH$ and $NaH_2PO_2$
$IV$. $NaHCO_3$ and $NaOH$

In good conductors of electricity,the type of bonding that exists is