The IPSec protocol is used to end-to-end security of data in which of the following layers of the Internet protocol suite

Answer options:

A.Application Layer
B.Transport Layer
C.Network layer
D.Link Layer

Answer - C
Refer link: 
https://aws.amazon.com/blogs/security/creating-an-opportunistic-ipsec-mesh-between-ec2-instances/
For more information on the IPSec protocol , one can visit the below URL:
https://en.wikipedia.org/wiki/IPsec