The correct answer is option 1. The first ionization energy, in group 15 elements in increasing atomic number, decreases. Ionization energy is the amount of energy requires to detach one electron from the atom. In the periodic table, the ionization energy decreases as one goes down.
The atomic number is the number of protons meaning that there are 14 protons in an atom of silicon. The mass number is the sum of the protons and neutrons. 28 - 14 = 14. There are 14 protons and 14 neutrons in silicon.
Some physical properties change, but the substance keeps its identity.
When dealing with these kind of questions, understand that the keyword here is physical change. Thus, all options that says no physical properties change are WRONG. So this leaves us with only 2 answers left. However, this is a physical change, no chemical change. Thus, the substance will keep its identity and not change.