Consider the following network of capacitors extended up to infinity and find the equivalent capacitance between P and Q.

Explanation

We can understand that the equivalent capacitance between P and Q must be the same as net capacitance between R and S due to the repeating nature of this network.
Let x be the net capacitance of this network between points P and Q then it must be same between R and S. We can understand it with the help of the following diagram.

`x=C+(2Cx)/(2C+x)`
`rArr x=(2C^(2)+Cx+2Cx)/(2C+x)`
`rArr 2Cx+x^(2)=2C^(2)+Cx+2Cx rArr x^(2)-Cx-2C^(2)=0`
`x= (Cpm sqrt(C^(2)+8C^(2)))/(2) rArr x=(Cpm 3C)/(2) rArr x=2C & -C`
2C is the correct answer.