Box 1: No -
VM1 is in Zone2 whereas the NAT Gateway is in Zone1. The VM would need to be in the same zone as the NAT Gateway to be able to use it. Therefore, VM1 cannot use the NAT gateway.
Box 2: Yes -
NATgateway1 is configured in the settings for Subnet2.
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