Explanation:
Box 1: Yes
You will not achieve zone redundancy with that setup, but it will work "While the scenario will appear to work, its health model and failure mode is undefined from an availability zone point of view".
https://docs.microsoft.com/en-us/azure/virtual-network/nat-gateway/nat-gateway-resource#cross- zone-outbound-scenarios-not-supported Box 2: No NAT GW has configured only 1 subnet and in Subnet1 Config you can clearly see that it is linked to NatGateway1. This is possible because subnets are not a zonal construct, i.e. not assigned to a zone.
Box 3: No
The NAT gateway does not have a single public IP address, it has an IP prefix which means more than one IP address. The VMs the use the NAT Gateway can use different public IP addresses contained within the IP prefix.
Reference:
https://docs.microsoft.com/en-us/azure/virtual-network/nat-gateway/nat-gateway-resource