Question

In a sample of ethyl ethanoate $\left({\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5\right)$ the two oxygen atoms have the same number of electrons but different number of neutrons. Which of the following is the correct reason for it?

• A. One of the oxygen atoms has gained electrons
• B. One of the oxygen atoms has gained two neutrons
• C. The two oxygen atoms are isotopes
• D. The two oxygen atoms are isobars.

Answer 1

The correct option is C

The two oxygen atoms are isotopes

Explanation for the correct answer:-

Option (C):- The two oxygen atoms are isotopes.

1. Isotopes are defined as the variants of a particular element.
2. These are basically the atoms of the same element having the same atomic number but a different mass numbers.
3. A number of electrons and protons are equal in an atom, but neutrons are different.
4. As in Ethyl ethanoate ${\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5$, two oxygen atoms are there have different neutrons.
5. Because of different neutrons present, they will have different mass numbers and will be considered isotopes.

Explanation for the incorrect answers:-

Option (A):- One of the oxygen atoms has gained electrons

1. The two oxygen atoms in Ethyl ethanoate $\left({\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5\right)$ are isotopes.
2. Because the two oxygen atoms are isotopes, so they will have same number of electrons and will not gain any.

Option (B):- One of the oxygen atoms has gained two neutrons.

1. Both the Oxygen atoms are isotopes, having same number of electron and proton but different number of neutrons.
2. For finding the neutron , subtract number of protons from the mass number of that particular isotope.
3. But there will not be any gain of neutrons in any isotope.

Option (D):- The two oxygen atoms are isobars.

1. Isobars are actually the atoms of the different elements which will have same mass number (nucleon) but different atomic number.
2. Nucleon is actually the sum of number of protons and neutrons which will remain same in the isobars.
3. But the two Oxygen atoms here have same atomic number, electrons and protons but different mass number and neutrons.
4. So, two Oxygen atoms here are isotopes and not isobars.

Therefore, the correct option is (C)- The two oxygen atoms are isotopes.