Third transition series starts with the element `"…............"` and ends at the element`"….............."`.

Answer

To determine the elements that mark the beginning and end of the third transition series, we need to understand the arrangement of transition metals in the periodic table.

### Step 1: Identify the starting element of the third transition series
The third transition series consists of the elements that fill the 4d subshell. The series begins with the element that has the atomic number 39, which is Yttrium (Y).

### Step 2: Identify the ending element of the third transition series
The third transition series ends with the element that has the atomic number 48, which is Cadmium (Cd). Cadmium is the last element in the 4d block.

### Final Answer
The third transition series starts with the element **Yttrium (Y)** and ends with the element **Cadmium (Cd)**.

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