Explanation:
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Hey there!
27 tells us the sum of protons and neutrons is 27.
Al tells us we have 13 protons.
3+ tells us that there are 3 less electrons than protons.
13 + n = 27
neutrons = 14
13 - 3 = 10 electrons
27Al3+ has 13 protons, 14 neutrons, and 10 electrons.
Hope this helps!
Let's eliminate these one by one.
The first pair would not be the same, as X would most likely be in group IA, and Y would be in group VIIA, because of their tendency to gain and lose electrons.
The second pair would also violate the same rule, but X would most likely be in group IIA, and Y would most likely be in group VIA.
The third pair would not be the same, as X is most likely in group VIIA, and since Y has eight valence electrons, it is most likely a noble gas.
The final pair has X with atomic number 15, making it phosphorous. Phosphorous wants to gain 3 electrons to have a full octet of 8 outer "valence" electrons, and Y would also like to gain 3 electrons. This means it is possible that the final pair would be in the same group.
For every 2 Mol NaOH you would get 1 Mol N2H4
