Which solution is more concentrated?
0.5 M NaCl
0.005 M NaCl
0.05 M Nacl
5.0 M NaCl

5.0 M NaCl

Explanation:

A concentrated solution is one which has more amount of solute in it.

A dilute solution is one which has less amount of solute in it.

Molarity is defined as the number of moles of solute present per liter of the solution.

0.5 M NaCl will have 0.5 moles of NaCl in 1 L of the solution, 0.005 M NaCl has 0.005 moles of NaCl in 1 L of the solution, 0.05 M NaCl has 0.05 moles of NaCl in 1 L and 5.0 M NaCl has 5 moles of NaCl in 1 L.

Thus 5.0 M NaCl will be most concentrated.

the answer for sodium is 0.186

the answer for rubidium is 0.251