An ideal gas of $N \operatorname{spin} \frac{1}{2}$ fermions is confined to a volume $V$. Calculate the zero temperature limit of (a) the chemical potential, (b) the average energy per particle, (c) the pressure, (d) the Pauli spin susceptibility. Show that in Gaussian units the susceptibility can be written as $3 \mu_{\mathrm{B}}^2 N / 2 \mu(0) V$, where $\mu(0)$ is the chemical potential at zero temperature. Assume each fermion has interaction with an external magnetic field of the form $2 \mu_0 H S_z$, where $\mu_{\mathrm{B}}$ is the Bohr magneton and $S_z$ is the $z$-component of the spin.