Answer
a.$_8^{18}O$
b.$_4^{9}Be$
c.$_{25}^{53}Mn$
d.$_{11}^{24}Na$
e.$_{28}^{60}Ni$
Work Step by Step
To answer this question you must study topic 4.4 ' Atomic number and Mass number' on page 114 and topic 4.5 ' Isotopes and Atomic Mass' on page 117.
The mass number is given by 'number of neutrons + number of protons' (10+8=18) and it goes above the element $^{18}O$. The atomic number (8 protons) goes below the element $_8^{18}O$.
