MCQ
In helium nucleus, there are
- A$2$ protons and $2$ electrons
- B$2$ neutrons, $ 2$ protons and $2$ electrons
- ✓$2$ protons and $2$ neutrons
- D$2$ positrons and $2$ protons
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| List$-I$ (Layer of atmosphere) | List$-II$ (Approximate height over earth's surface) |
| $(A)$ $F_1$ - Layer | $(I)$ $10\,km$ |
| $(B)$ $D-$ Layer | $(II)$ $170-190\,km$ |
| $(C)$ Troposphere | $(III)$ $100\,km$ |
| $(D)$ $E-$layer | $(IV)$ $65-75\,km$ |
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