Answer:

Step-by-step explanation:
Since, we know that,
The surface area of a cylinder having both ends in both sides,

Where,
r = radius,
h = height,
Given,
Diameter of the sphere = 4 cm,
So, by using Pythagoras theorem,
( see in the below diagram ),



Thus, the surface area of the cylinder,

Differentiating with respect to r,



Again differentiating with respect to r,

For maximum or minimum,






Since, for r = √2,

Hence, the surface area is maximum if r = √2,
And, maximum surface area,



