Please help me, Thank you!

5

Explanation:

The electrons in the outermost shell are the valence electrons. Since there are 5 electrons in the third energy level, there are 5 valence electrons.

Hope that helps.

Explanation:

Hello,

At first, it turns out convenient to compute the total moles of sodium that will be dissolved into the solution by considering the added amounts of sodium bromide and sodium sulfate:

Once we've got the moles we compute the final volume via:

Thus, the molarity of the sodium atoms turn out into:

Now, we perform the same procedure but now for the bromide ions:

Finally, its molarity results:

Best regards.