In which of the following compounds does the transition metal have a zero oxidation state?

In the extraction of aluminium:
Process $X$: applied for red bauxite to remove iron oxide (chief impurity).
Process $Y$: (Serpeck's process) applied for white bauxite to remove $Z$ (chief impurity). Then,process $X$ and impurity $Z$ are:

In the figure $(a)$,half of the meter scale is made of wood while the other half is made of steel. The wooden part is pivoted at $O$. $A$ force $F$ is applied at the end of the steel part. In figure $(b)$,the steel part is pivoted at $O'$ and the same force is applied at the wooden end (in a horizontal plane).

$A$ complex of platinum,ammonia,and chloride produces four ions per molecule in the solution. The structure consistent with this observation is:

Two short magnets $AB$ and $CD$ are in the $X-Y$ plane and are parallel to the $X$-axis. The coordinates of their centers are $(0,2)$ and $(2,0)$ respectively. The line joining the north-south poles of $CD$ is opposite to that of $AB$ and lies along the positive $X$-axis. The resultant magnetic field induction due to $AB$ and $CD$ at point $P(2,2)$ is $100 \times 10^{-7} \ T$. When the poles of the magnet $CD$ are reversed,the resultant magnetic field induction is $50 \times 10^{-7} \ T$. The values of the magnetic moments of $AB$ and $CD$ (in $Am^2$) are:

Natural gas is a mixture of .........?