NCERT Exemplar IX — task. Science CBSE, Class 9.

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1. Is it possible for the atom of an element to have one electron, one proton and no neutron. If so, name the element.

No, there is no element as such.
Yes, helium has \(1\) electron, \(1\) proton and no neutron. It is represented as \(_{1}\textrm{He}^{2}\).
Yes, hydrogen has \(1\) electron, \(1\) proton and no neutron. It is represented as \(_{1}\textrm{H}^{1}\).

2. Will \(_{}\textrm{Cl}^{35}\) and \(_{}\textrm{Cl}^{37}\) have different valencies? Justify your answer.

No, both \(_{}\textrm{Cl}^{35}\) and \(_{}\textrm{Cl}^{37}\) will have same valencies as they are isotopes.
No, both \(_{}\textrm{Cl}^{35}\) and \(_{}\textrm{Cl}^{37}\) will have same valencies as they are isotones.
Yes, both \(_{}\textrm{Cl}^{35}\) and \(_{}\textrm{Cl}^{37}\) will have different valencies as they are isotopes.

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