What is the mixture of $MgCl_2$ and $MgO$ called?

The enthalpies of combustion of carbon and carbon monoxide are $-393.5 \, kJ \, mol^{-1}$ and $-283.0 \, kJ \, mol^{-1}$ respectively. Calculate the enthalpy of formation of carbon monoxide in $kJ \, mol^{-1}$. (in $.5$)

The four arithmetic means between $3$ and $23$ are

$A$ person moves $30\, m$ north and then $20\, m$ towards east and finally $30\sqrt{2}\, m$ in south-west direction. The displacement of the person from the origin will be

The number of lone pairs of electrons present on $Xe$ in $XeF_4$ is

The $pK_a$ of a weak acid is $4.8$. What should be the ratio of $\frac{[\text{acid}]}{[\text{salt}]}$,if a buffer of $pH=5.8$ is required?