Elements in a period have same

Options

A. number of valence electrons
B. valency
C. number of shells
D. volume

Answer

### Step-by-Step Solution

1. **Understanding Periods in the Periodic Table**:
- The periodic table is organized into rows called periods and columns called groups. There are 7 periods in the modern periodic table, as defined by Moseley.

2. **Identifying Elements in a Period**:
- Each period contains elements that are arranged in order of increasing atomic number. For example, in period 2, the elements include lithium (Li), beryllium (Be), boron (B), carbon (C), nitrogen (N), oxygen (O), fluorine (F), and neon (Ne).

3. **Atomic Number and Protons**:
- The atomic number of an element is equal to the number of protons in its nucleus. As you move across a period from left to right, the atomic number increases, which means the number of protons also increases.

4. **Electron Configuration**:
- For a neutral atom, the number of electrons equals the number of protons. As you move across a period, while the number of electrons increases, the last electron added will occupy the same energy shell (or principal quantum level).

5. **Number of Shells in Elements of a Period**:
- All elements in a given period have the same number of electron shells. For instance, all elements in period 2 have 2 electron shells, while all elements in period 3 have 3 electron shells.

6. **Conclusion**:
- Therefore, the elements in a period have the same number of electron shells.

### Final Answer
Elements in a period have the same number of electron shells.

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