Answer
$^{8}_{16} O$
$^{8}_{17} O$
$^{8}_{18} O$
Work Step by Step
Atomic number is the number of protons and electrons.
Number of neutrons = mass number $-$ atomic number
Oxygen has an atomic number of 8. In order to have 8 neutrons it should have mass number 16 ( $16-8= 8 neutrons$) Thus, first isotope is $^{8}_{16} O$
Oxygen has an atomic number of 8. In order to have 9 neutrons it should have mass number 17 ( $17-8= 9 neutrons$) Thus, first isotope is $^{8}_{17} O$
Oxygen has an atomic number of 8. In order to have 10 neutrons it should have mass number 18 ( $18-8= 10 neutrons$) Thus, first isotope is $^{8}_{18} O$
