Explanation:
No, No, No
Comprehensive and Detailed 150 to 250 words of Explanation From [Microsoft Azure Administrator/Course Guide/topics]:
Although VNet1 and VNet2 are peered, routing must be valid in both directions for ping to succeed. Azure virtual network peering enables private connectivity between peered virtual networks, and Azure adds virtual network peering system routes when peering is configured. However, user-defined routes override system routes when they conflict, and Azure selects routes by longest prefix match before applying route-source priority.
VM11 can send traffic toward VM2 through the VNet1-to-VNet2 peering route, but VM2's return traffic to VM11 matches Route2 in RT2: destination 10.10.1.0/24, next hop type None. Microsoft defines None as dropping traffic rather than forwarding it, so the ping fails. VM2 also cannot initiate a successful ping to VM11 for the same reason: its outbound traffic to 10.10.1.10 is dropped by Route2. VM3 cannot ping VM12 because VNet3 is not peered with VNet1, and Route3 points to a virtual appliance IP in a network without direct connectivity. Microsoft specifies that a virtual appliance next hop IP requires direct connectivity, otherwise the UDR configuration is invalid. Study Guide reference: AZ-104 Configure and manage virtual networking , routing, route tables, and virtual network peering.

Explanation:

In Microsoft Azure, connectivity between virtual networks depends on IP address space, region, and subscription constraints.
1## Site-to-Site VPN between VNET1 and VNET2 - YES:
Azure supports a Site-to-Site VPN connection between two VNets in different regions or subscriptions as long as both have non-overlapping address spaces and contain a VPN gateway. In this case, VNET1 (10.10.10.0/24 - West Europe) and VNET2 (172.16.0.0/16 - West US) have unique address spaces, so a S2S connection is possible.
2## VNET1 and VNET2 Peering - YES:
VNet peering enables direct communication over the Microsoft backbone network with low latency and no gateway requirement. Global VNet Peering supports VNets in different Azure regions (e.g., West Europe and West US) as long as address spaces do not overlap-which is true here.
3## VNET1 and VNETA Peering - NO:
VNETA's address space (10.10.128.0/17) overlaps with VNET1 (10.10.10.0/24), because both belong to the same 10.10.0.0/8 range. Azure explicitly blocks VNet peering between VNets with overlapping address spaces to avoid routing conflicts.
According to Microsoft Learn ("Virtual network peering - requirements and constraints"), peering is only supported when address spaces do not overlap. Therefore, VNET1 and VNETA cannot be peered.