Rapid growth in telemetry that demands scalable infrastructure is the correct option because adding hundreds of thousands of sensors typically creates a large and sustained increase in data volume that must be ingested, stored, processed, and analyzed.

Rapid growth in telemetry that demands scalable infrastructure forces architects to plan for high ingest rates, greater message throughput, horizontal scaling of brokers and stream processors, cost implications for storage and egress, and operational challenges for monitoring and alerting.

Cloud Pub/Sub is not a disadvantage by itself because it is a messaging service that can help buffer and route telemetry. The option names a product rather than a drawback and it therefore does not describe a likely disadvantage of scaling an IoT deployment.

Less complex network topology is incorrect because scaling to hundreds of thousands of endpoints usually increases network complexity. Larger fleets require more routing, segmentation, and management, so the topology tends to become more complex not less.

Stronger endpoint protection is wrong because adding many devices normally increases the attack surface and makes consistent endpoint hardening more difficult. Large scale deployments require more effort to maintain and verify security rather than automatically producing stronger protection.

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