Option B Is Risky:
. A Scheduleable and Batchable class that queries the Catalog object and updates the Catalog Items if the Catalog CurrencyIsoCode is different

Querying Catalogs and then loading all their children (up to millions total) in execute() will likely:
Hit query row limits (50k total rows across SOQL queries).
Cause heap size issues or CPU timeouts if too many Catalog Items are loaded per Catalog.
❌ Poor fit for a parent-to-child large-volume use case.
❌ You can't guarantee CatalogItem[] processing stays within batch-safe limits.

Option A is Correct. A Scheduleable and Batchable class that queries the Catalog Item object and updates the Catalog Items if the Catalog CurrencyIsoCode is different

You batch directly on Catalog Items, which allows you to process children in manageable 200-record chunks.
This keeps you safely under the 50,000-row query limit per transaction.
In each batch, you can reference the parent Catalog (via CatalogId) and compare the CurrencyIsoCode before updating.
✅ Scalable even when 1 Catalog has >50k children.
✅ You stay within Apex limits by controlling batch size and records per execution.

Correct answer is Option A. Reason: You have to do this via asynchronous since the data volume is high to process & you have to query child records in batch since a parent can have lakhs of child data which you cannot process in execute in any single batch chunks

Hello Admin, please delete my previous comment for this question. This question is already marked correct answer. Answer is B only.

Answer should be D.