To solve, find the oxidative states of the other molecules in the compound, sum them, and then Chlorine’s charge will be equal to the opposite charge of that number (i.e if other molecules summed charged = -1, then chlorine will have a charge of +1. Why? In neutral compounds, the total oxidative number must be equal to 0).
Cl_2O : Oxygen is a group 6 non metal, and will have an oxidative state of -2. Cl_2 - 2 = 0
Cl_2 = +2
Cl = +1
KCl : Potassium is a group 1 alkali metal, and will have an oxidative state of +1
Cl = -1
KClO : Potassium has an oxidative state of +1, oxygen has an oxidative state of -2.
1 + Cl - 2 = 0
Cl = +1
KClO_3 : Potassium has an oxidative state of +1, oxygen has an oxidative state of -2.
1 + Cl + (3)(-2) = 0
Cl - 5 = 0
Cl = 5
KClO_4 : Potassium has an oxidative state of +1, oxygen has an oxidative state of -2.
1 + Cl + (4)(-2) = 0
Cl - 7 = 0
Cl = +7
Cl_2O_7 : oxygen has an oxidative state of -2.
Cl_2 + (7)(-2) = 0
Cl = +7
\fcolorbox{red}{grey!30}{Therefore the answer is D, $-1, 0, +1, +5, +7$}