To determine which statements about the elements P, Q, R, and S are correct, we will analyze each statement based on the given electronic configurations.
### Given Electronic Configurations:
- **P:** 2, 8, 1
- **Q:** 2, 5
- **R:** 2, 8, 7
- **S:** 2, 8, 5
### Analyzing Each Statement:
#### Statement I: Elements Q and S belong to the same period of the periodic table.
- **Analysis:**
- Element Q has an electronic configuration of 2, 5, which means it has 2 shells (K and L).
- Element S has an electronic configuration of 2, 8, 5, which means it has 3 shells (K, L, and M).
- Since Q has 2 shells and S has 3 shells, they belong to different periods.
- **Conclusion:** **False**
#### Statement II: P is an alkali metal.
- **Analysis:**
- The electronic configuration of P is 2, 8, 1. Alkali metals are characterized by having one electron in their outermost shell.
- P has one valence electron, which confirms it is an alkali metal.
- **Conclusion:** **True**
#### Statement III: R is a metal.
- **Analysis:**
- The electronic configuration of R is 2, 8, 7. This means R has 7 electrons in its outermost shell.
- Metals typically have 1 to 3 electrons in their outer shell and tend to lose electrons to form positive ions. With 7 valence electrons, R is more likely to gain electrons and behave like a non-metal.
- **Conclusion:** **False**
#### Statement IV: Valency of element S is 3.
- **Analysis:**
- The electronic configuration of S is 2, 8, 5. The number of valence electrons is 5.
- To find the valency, if the number of valence electrons is greater than 4, we subtract it from 8:
- Valency = 8 - 5 = 3.
- **Conclusion:** **True**
### Summary of Statements:
- **I:** False
- **II:** True
- **III:** False
- **IV:** True
### Correct Statements:
The correct statements are II and IV.
### Final Answer:
The correct statements are II and IV.
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