Answer:
Question (a):
Answer: 2:8:7
Step-by-step explanation: Chlorine, Cl is in period 3 hence two energy levels [ 2:8:_]. Chlorine is in group IV (halogen) hence it has 7 outermost energy level electrons. Hence deducing 2:8:7
Question (b)
» (i): Carbon and silicon [ C and Si ]
A group is a column in a periodic table
» (ii): Silicon and Chlorine [ Si and Cl ]
A period is a row in a periodic table
» (iii): Hydrogen and Chlorine [ H and Cl ]
It forms hydrogen chloride gas. When this gas is passed on warm water or steam, hydrochloric acid is formed.
» (iv): Chlorine [ Cl ]
An element has electron number equivalent to group number. Group I elements have one electron, Group ii elements have two electrons and so on.
Helium is in group Viii but in period 1, so it has eight electrons.
But chlorine has seven outermost electrons but since it is in period 3, its electrons are 8 + 7 = 15 electrons.
» (v): Chlorine [ Cl ]
Chlorine only lacks one electron to become full and stable. So it is assigned by Cl- (-1)