Here's why:

* Central atom: The central atom in C2H5Cl is the carbon atom bonded to the chlorine atom.

* Hybridization: This carbon atom has four electron domains (one single bond to the chlorine atom, one single bond to the other carbon atom, and two single bonds to hydrogen atoms). This means it undergoes sp3 hybridization.

* Shape: Sp3 hybridization results in a tetrahedral geometry, meaning the central carbon atom is at the center of a tetrahedron with its four bonds pointing towards the corners.

Note: While the overall molecule isn't strictly tetrahedral due to the presence of the other carbon atom, the carbon directly bonded to chlorine exhibits tetrahedral geometry around it.