Answer to Question 1
Moseley's work on characteristic x-ray spectra determined that the number of protons, not the whole atomic weight A of the nucleus, was the most important factor in chemical bonding and in ordering the periodic table
Answer to Question 2
C.
Their work was so important at the time because it affirmed Planck's work to be true, that nature does exhibit quantization. The key cases involved could only be explained by quantum physics, and showed its triumph over classical physics.