1. Recall that when a photon is absorbed, electrons 'jump' up energy levels. We can thus rule out B and D.
We can then use the formula \(E= \frac{hc}{\lambda}\) to find the value of the energy change, which just so happens to be equivalent to the difference between levels 1 and 3 - hence, the answer is A.
2. Try to target these sorts of questions in the exam! The decay constant is equal to \(\frac{\ln 2}{t_\frac{1}{2}}\). observe from the graph that the initial sample is 5g, so the half life is the time it takes to go down to 2.5g, which is about 29 years. Putting it into the calculator with that formula will get you an answer close to D.
3. Recall that when beta decay occurs, a neutron 'splits' into a proton and an electron (simplistically, kinda true). The electron is released (beta particle!) and the proton latches on to the nucleus. This means that there is one more proton and one less neutron. In heavier elements the ratio of protons to neutrons is about 1:1.5, so this will cause the ratio to go closer to 1:1 ie. towards the n=p line. Hence, the answer is A.