Answer
a) $-2$
b) $+3$
c) $+4$
d) $-1$
Work Step by Step
When an element possess more electrons than protons, then the element is an anion (has a negative charge).
When an element possess fewer electrons than protons, then that element is a cation (has a positive charge).
a) Oxygen has an atomic number of 8. But in this case, it is possessing 10 electrons. Since number of electrons $\gt$ No. of protons. Therefore it has a charge of $-(10-8)$ $= -2$
b) Aluminium has an atomic number of 13. But in this case, it is possessing 13 electrons. Number of electrons $\lt$ number of protons, so it has a charge of $+(13-10)$ $= +3$
c) Titanium has an atomic number of 22. But, in this case, it is possessing 18 electrons. Number of electrons $\lt$ number of protons. Therefore, so it has a charge of $+(22-18)$ $= +4$
d) Iodine has an atomic number of 53. But in this case, it is possessing 54 electrons. Number of electrons $\gt$ number of. Therefore it has a charge of $-(54-53)$ $= -1$