Because if you have a liquid then you need a glass to keep it together and when it is a solid it is already together so you don't need to do anything
You have to add a photo to we can understand - Yuno Gasai
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.
They'd observe any new substances or new color, and temp. that is irreversible.
If this helped and you have any other questions, feel free to comment on my wall. Hope this helped.
