The correct option is Create one subnet in each of at least two Availability Zones and deploy instances across those subnets.

This approach places resources in separate Availability Zones so the service can continue running if one AZ fails. It pairs naturally with an Auto Scaling group and a load balancer to distribute traffic and replace failed instances. Subnets are scoped to AZs and creating one subnet per AZ is the mechanism that lets you place instances in multiple AZs for resilience.

Attach a dedicated Internet Gateway to each Availability Zone is incorrect because an Internet Gateway attaches to the VPC rather than to individual AZs. You can only have one Internet Gateway per VPC and creating additional IGWs would not provide AZ level fault tolerance.

Use a spread placement group for the EC2 instances is incorrect because placement groups influence how instances are placed on underlying hardware and they do not provide multi AZ networking. You still need distinct subnets in different AZs to survive an AZ outage.

Create several subnets that all reside in the same Availability Zone is incorrect because keeping all subnets in one AZ leaves the service vulnerable to a single AZ failure. High availability requires spanning multiple Availability Zones.

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