The correct answer is C. 100 mm.
The minimum overall depth of a slab to satisfy vertical deflection limits is determined by the following equation:
$d = \frac{L^2}{240 f’_c b}$
where:
- $d$ is the minimum overall depth of the slab (in mm)
- $L$ is the clear span of the slab (in mm)
- $f’_c$ is the compressive strength of the concrete (in MPa)
- $b$ is the width of the slab (in mm)
For a continuous slab of 3 m x 3.5 m size, the clear span of the slab is 3 m. Assuming a compressive strength of concrete of 25 MPa and a width of slab of 3.5 m, the minimum overall depth of the slab is:
$d = \frac{3^2}{240 \times 25 \times 3.5} = 100$ mm
Therefore, the minimum overall depth of slab to satisfy vertical deflection limits is 100 mm.
Option A is incorrect because it is less than the minimum required depth. Option B is incorrect because it is less than the minimum required depth. Option D is incorrect because it is greater than the minimum required depth.