Write the atomic number of the element in which the filling of 3d-subshell in the atom just starts.

Explanation

To determine the atomic number of the element in which the filling of the 3d-subshell in the atom just starts, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Order of Electron Filling**: According to the Aufbau principle, electrons fill atomic orbitals in order of increasing energy levels. The order of filling is:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, etc.

2. **Count Electrons in Each Subshell**:
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