Introduction:
When light passes through a medium with a different refractive index, it bends or refracts. The amount of bending depends on the refractive indices of the two media and the thickness of the medium. In this case, we have a glass slab with a bubble inside it, and we are given the positions of the bubble when viewed from both sides of the slab. From this information, we can determine the thickness of the slab.

Given:
Refractive index of the glass slab = 1.5
Position of the bubble when viewed from one side = 5 cm
Position of the bubble when viewed from the other side = 2 cm

Calculating the thickness of the slab:
To calculate the thickness of the slab, we need to understand the concept of apparent depth.

Apparent depth:
When light travels from one medium to another, it changes its speed and direction. This change in direction can create the illusion that an object is at a different position than its actual position. This apparent position is known as the apparent depth.

Formula for apparent depth:
The formula for apparent depth is given by:
Apparent depth = Actual depth / Refractive index

Calculating the actual depth of the bubble:
Let the actual thickness of the slab be 'd' cm.
When the bubble is viewed from one side, the apparent depth is 5 cm and the refractive index is 1.5. Using the formula for apparent depth:
5 = d / 1.5

When the bubble is viewed from the other side, the apparent depth is 2 cm and the refractive index is 1.5. Using the formula for apparent depth:
2 = d / 1.5

Solving the equations:
From the first equation, we can rearrange it to find the actual depth:
d = 5 * 1.5 = 7.5 cm

From the second equation, we can rearrange it to find the actual depth:
d = 2 * 1.5 = 3 cm

Conclusion:
We have found two different values for the actual depth of the bubble, which is not possible. This indicates that there is an error in the given information or the calculations. Therefore, it is not possible to determine the thickness of the slab with the given information.