Basic question ....Interviewers question?

In this particular design, generate ICMP traffic for pc B (20.1.1.1) from pc A (10.1.1.1). 

First, pc A will send ARP request for default gateway 20.1.1.1 & pc B will ARP reply with its MAC address.

Now, pc A has got the MAC address of 20.1.1.1 & the ICMP encapsulation is complete. Hence, both the devices will communicate. 

They don't communicate to each other. Because both are in a different network which signified by its IP address, to connect two different networks we need a router. If a router is placed between them, rather than they don't communicate coz of  default gateway address given to end devices are differ than its ip address, which belongs to another network.