How to prove that reaction is possible
The ionic equation for this reaction is:

$\ce{Fe + 2H+ ~(+\;SO4^2- ) -&gt; Fe^2+ + H2 ~(+\;SO4^2- )}$

As two half-reactions, it is seen that the iron is oxidized:

$\ce{Fe -&gt; Fe^2+ + 2e- }$

The reductant (iron) transfers electrons to hydrogen, and is thus itself oxidized.

And the hydrogen is reduced:

$\ce{2H+ + 2e- -&gt; H2}$

The oxidant (hydrogen) removes electrons from iron, and is thus itself reduced.

To calculate the reduction potential you have to solve the following equation:

$\Delta E = E_\text{acceptor} - E_\text{donor} = E_{\ce{2H+/H2}}- E_{\ce{Fe/Fe^2+}}$

$\Delta E = 0\ \mathrm{V} - (-0.41\ \mathrm{V}) = 0.41\ \mathrm{V}$

The reactions runs voluntarily if $\Delta E &gt; 0$.

You can do the same for b).