The answer is Strontium(Sr). The reactive increase from right to left. And this element has two valence electrons. So Rb is not correct. Then the very reactive metal is Sr.
Calculate the ratio by using Henderson-Hasselbalch equation:
pH = pKa + log [neutral form] / Protonated form
3.05 = 2.21 + log [neutral form] / [Protonated form]
3.05 - 2.21 = log [neutral form] / [Protonated form]
0.84 = log [neutral form] / [Protonated form]
[neutral form] / [protonated form] = anti log 0.84 = 6.91
Molarity= moles/liter, so you would need 3mol KBr/1 liter
(0.3M)(1L)= 0.3mol KBr
Within the core of the Sun, temperatures and pressures are high enough to fuse hydrogen atoms into helium, which is the Sun's main form of energy production. Assuming there was a slight mistake in where you have copied the results here the correct answer is the third option.
Hope this helps!