Question

Which from following is NOT hydrogen like species?

• A. \(\text{Li}^{+2}\)
• B. \(\text{Be}^{+3}\)
• C. \(\text{Li}^{+}\)
• D. \(\text{He}^{+}\)

Hint:

Hydrogen-like species always contain exactly one electron, for example: \[ \text{He}^+,\ \text{Li}^{2+},\ \text{Be}^{3+} \]

Answer 1

The Correct Option is C

Concept:
A hydrogen-like species is a one-electron species. So, to identify a hydrogen-like species, we check whether only one electron is present.

Step 1: Check \(\text{Li}^{2+}\).
Lithium has atomic number \(3\), so neutral Li has \(3\) electrons. \[ \text{Li}^{2+} \Rightarrow 3-2=1 \text{ electron} \] So it is hydrogen-like.

Step 2: Check \(\text{Be}^{3+}\) and \(\text{He}^{+}\).
For \(\text{Be}^{3+}\): \[ 4-3=1 \text{ electron} \] For \(\text{He}^{+}\): \[ 2-1=1 \text{ electron} \] So both are hydrogen-like.

Step 3: Check \(\text{Li}^{+}\).
\[ \text{Li}^{+} \Rightarrow 3-1=2 \text{ electrons} \] So \(\text{Li}^{+}\) is not hydrogen-like. Hence, the correct answer is:
\[ \boxed{(C)\ \text{Li}^{+}} \]