MCQ
The ratio of the velocity of electron in the ground state of hydrogen atom and its velocity in second excited state of $He^+$ ion is
- A$3.5$
- ✓$1.5$
- C$2$
- D$2.5$
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| Period number | Group number | |
| $P$ | $2$ | $15$ |
| $Q$ | $3$ | $2$ |
Then formula of the compound formed by $P$ and $Q$ element is