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1. I have the following question attached.

The way I calculated this was by doing 25/1000 * 6.02 * 10^23 and then recognising that there were three ions, 2 Na + and and So4 2- ions, so the final operation was:

25/1000 * 6.02 * 10^23 * 3 = 2.26 x 10^21 (A)

But this is apparently wrong and the correct answer is (B) as I should have not multiplied by three at all and left the sum as

25/1000 * 6.02 * 10^23 = 7.53 * 10^20.

Why?
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2. The correct is A.
3. A is the correct answer

no of moles of Na2SO4 = 0.05 x 25/1000
= 1.25 x 10^-3

no of moles of ions = 3 x 1.25 x10^-3

= 3.75 x 10^-3

so total no of ions = 6.02 x 10^23 x 3.75 x 10^-3

= A

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