A nuclide X is an isotope of \( {}^{16}_{8}\mathrm{O} \) and an isotone of \( {}^{18}_{9}\mathrm{F} \). The nuclide X is
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \( {}^{17}_{8}\mathrm{O} \)
Isotopes have the same atomic number \( Z \), and isotones have the same neutron number \( N=A-Z \). X is an isotope of \( {}^{16}_{8}\mathrm{O} \), so it has \( Z=8 \). Its neutron number equals that of \( {}^{18}_{9}\mathrm{F} \):
\( \begin{aligned} N &= 18-9 \\ &= 9 \end{aligned} \)
The mass number of X is then:
\( \begin{aligned} A &= Z+N \\ &= 8+9 \\ &= 17 \end{aligned} \)
Hence, X is \( {}^{17}_{8}\mathrm{O} \).
NCERT (2026-27):
Summary – “Nuclides with the same atomic number Z, but different neutron number N are called isotopes. Nuclides with the same A are isobars and those with the same N are isotones.”