Step 1: Note the claims.
Assertion: a large share of the Chhattisgarh budget goes to the social sector. Reason: the state gives priority to welfare schemes.
Step 2: Recall how budgets reflect priorities.
A state's spending pattern mirrors the policy goals it sets.
Step 3: Verify the Assertion.
Chhattisgarh allocates heavily to education, health, food security, and tribal welfare, so the Assertion is true.
Step 4: Verify the Reason.
The state indeed emphasises welfare schemes for poverty reduction and inclusive growth, so the Reason is true.
Step 5: Link them.
Prioritising welfare schemes directly drives the larger social-sector allocation, so the Reason explains the Assertion.
Step 6: Choose the label.
Both true and Reason explains Assertion, which is option A.
\[ \boxed{\text{Both [As] and [R] are true, and [R] is the correct explanation of [As].}} \]