Explanation:
First, we need to calculate the molarity of both solutions. The solution with higher molarity is more concentrated.
Solution A:
First, let's transform 50.0 g of CaCO3 into moles using n = m/MM
MM of CaCO3 = 100 g/mol
n = 50/100
n = 0.5 moles
M = n/V
n = 0.5 moles
V = 250 mL = 0.25 L
M = 0.5/0.25
M = 2 mol/L
Solution B:
M = n/V
M = 6/2
M = 3 mol/L
Solution B has a higher molarity than solution A, which means that solution B is more concentrated.
Answer: Solution B.