The value of CFSE (Crystal Field Stabilization Energy) in a tetrahedral complex with a 3d^4 configuration of a metal ion surrounded by weak field ligands can be determined by considering the electronic configuration and the ligand field splitting.

1. Electronic Configuration:
In a 3d^4 configuration, there are four electrons occupying the five d-orbitals of the metal ion. The electronic configuration can be represented as (t2g)^4(eg)^0, where t2g represents the lower energy d-orbitals (dxz, dyz, and dz^2) and eg represents the higher energy d-orbitals (dx^2-y^2 and dxy).

2. Ligand Field Splitting in Tetrahedral Complexes:
In tetrahedral complexes, the ligands approach the metal ion along the axes between the d-orbitals, resulting in a different ligand field splitting compared to octahedral complexes. The energy difference between the t2g and eg orbitals is smaller in tetrahedral complexes, leading to weaker ligand field splitting.

3. Calculation of CFSE in Tetrahedral Complexes:
The CFSE in tetrahedral complexes can be calculated using the formula:
CFSE = -0.4 Δt (n(t2g) - n(eg))

- Δt represents the ligand field splitting parameter, which is positive for weak field ligands.
- n(t2g) represents the number of electrons in the t2g orbitals.
- n(eg) represents the number of electrons in the eg orbitals.

In a 3d^4 configuration, all four electrons occupy the t2g orbitals. Therefore, n(t2g) = 4 and n(eg) = 0.

Substituting these values into the CFSE formula:
CFSE = -0.4 Δt (4 - 0)
CFSE = -1.6 Δt

4. The Value of CFSE:
From the calculation, we can conclude that the value of CFSE in a tetrahedral complex with a 3d^4 configuration of a metal ion surrounded by weak field ligands is -1.6 Δt.

Answer: The value of CFSE in this case is -1.6 Δt.

Note: It is important to mention that the CFSE value depends on the ligand field splitting parameter (Δt), which is specific to the ligands involved in the complex. The given answer is a general representation assuming weak field ligands. The actual value can vary depending on the specific ligands present in the complex.