In a sample of ethyl ethanoate (CH₃COOC₂H₂), 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?

39

The radioactive isotope used in the treatment of cancer is:

40

Elements having valency ‘one’ are:

42

Which of the following elements does not exhibit electrovalency?

43

The number of valence electrons in a graphite atom is: