In the fourth period of the periodic table, how many elements have one or more 4d electrons:

Options

A. 2
B. 18
C. 0
D. 6

Answer

To solve the question of how many elements in the fourth period of the periodic table have one or more 4d electrons, we can follow these steps:

### Step 1: Identify the elements in the fourth period
The fourth period of the periodic table includes elements with atomic numbers from 19 (Potassium, K) to 36 (Krypton, Kr). This gives us a total of 18 elements.

### Step 2: Understand the electron configuration of the fourth period elements
The general electron configuration for the elements in the fourth period can be expressed as follows:
- The filling order begins with the 4s subshell, followed by the 3d subshell, and then the 4p subshell.
- The electron configurations for the fourth period elements are:
- 4s: can hold up to 2 electrons (4s²)
- 3d: can hold up to 10 electrons (3d¹⁰)
- 4p: can hold up to 6 electrons (4p⁶)

### Step 3: Determine the presence of 4d electrons
- The 4d subshell starts filling after the 5s subshell in the fifth period of the periodic table.
- Therefore, in the fourth period, there are no 4d electrons present in any of the elements.

### Step 4: Conclude the number of elements with 4d electrons
Since the fourth period does not contain any elements with 4d electrons, the answer to the question is zero.

### Final Answer
The number of elements in the fourth period of the periodic table that have one or more 4d electrons is **0**.

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