Answer
a) $+6$
b) $-2$
c) $-3$
d) $+2$
Work Step by Step
When an element possess more electrons than protons (or the atomic number), then the element is an anion (has a negative charge).
When an element possess fewer electrons than protons (or atomic number), then that element is a cation (has a positive charge).
a) Tungsten has an atomic number of 74. But in this case, it is possessing 68 electrons. Here, number of electrons $\lt$ number of protons. Therefore it has a charge of $+(74-68) =+6$
b) Tellurium has an atomic number of 52. But in this case, it is possessing 54 electrons. Since number of $\gt$ number of protons, it has a charge of $-(54-52) =-2$
c) Nitrogen has an atomic number of 7. But in this case, it is possessing 10 electrons. Since number of electrons $\gt$ number of protons, it has a charge of $-(10-7) =-3$
d) Barium has an atomic number of 56. But in this case, it is possessing 54 electrons. Here, number of electrons$\lt$ number of protons. Therefore, it has a charge of $+(56-548) =+2$
