Final answer:
The alkaline earth metal that has a higher atomic number than rubidium (Rb) but fewer neutrons than rhodium (Rh) is Barium (Ba). Barium has an atomic number of 56 and approximately 81 neutrons, which satisfies the conditions set in the question.
Step-by-step explanation:
The question asks for an alkaline earth metal that has a higher atomic number than rubidium but fewer neutrons than rhodium. Rubidium has an atomic number of 37, so we are looking for an alkaline earth metal with an atomic number greater than that. Rhodium has an atomic number of 45 and a standard atomic weight of about 102.91, which implies it typically has around 58 neutrons (since neutron count equals atomic weight minus atomic number).
Looking at the options provided (Strontium, Barium, Calcium, Magnesium), Strontium (Sr) has an atomic number of 38 and Barium (Ba) has an atomic number of 56. Since Strontium's atomic number is higher than Rubidium but Barium's atomic number is higher still, we can eliminate Strontium and move to investigate Barium.
Barium has an atomic weight of about 137.33, which would give it around 81 neutrons on average (137 minus 56). So Barium (Ba) is the alkaline earth metal that fits the conditions of having a higher atomic number than Rubidium and fewer neutrons than Rhodium.