Step 1: Use the density relation for an ideal gas.
The density of a gas is given by
\[
d=\frac{PM}{RT}
\]
where
\[
P=\text{pressure},
\quad
M=\text{molar mass},
\quad
R=\text{gas constant},
\quad
T=\text{temperature}
\]
For methane, \(M\) and \(R\) are constant.
Therefore,
\[
d\propto \frac{P}{T}
\]
Step 2: Analyze the effect of pressure and temperature.
Density increases with increase in pressure.
Density decreases with increase in temperature.
Hence, maximum density will occur at the highest pressure and the lowest temperature.
Step 3: Compare the given options.
Among the given options:
\[
0^\circ C = 273\ K
\]
and
\[
273^\circ C = 546\ K
\]
The lowest temperature is
\[
0^\circ C
\]
and the highest pressure is
\[
3\ \text{bar}
\]
Therefore, the maximum value of
\[
\frac{P}{T}
\]
occurs for
\[
0^\circ C,\ 3\ \text{bar}
\]
Step 4: Final conclusion.
Hence, methane has maximum density at
\[
\boxed{0^\circ C,\ 3\ \text{bar}}
\]
Therefore, the correct option is (4).