Step 1: Read both statements.
Assertion (A) says income-tax is levied on the total income of a person for the previous year. Reason (R) says income earned in the previous year is taxed in the immediately following assessment year under the Income-tax Act, 1961. We must judge if both are true and if R explains A.
Step 2: Check Assertion (A).
The Act charges tax on the total income earned in the previous year, which is the year in which the income is actually earned. So Assertion (A) is true.
Step 3: Check Reason (R).
The Act follows a system where the income of the previous year is assessed and taxed in the next year, called the assessment year. So Reason (R) is also true.
Step 4: See if R explains A.
The previous year income becomes the base for tax precisely because the Act says the assessment happens in the following year. So R gives the reason why A is true. R correctly explains A.
Step 5: Remove the wrong options.
Saying R does not explain A (option 1) is wrong, saying A is false (option 2) is wrong, and saying R is false (option 3) is wrong, because both are true and connected.
Step 6: State the answer.
So both (A) and (R) are true and (R) is the correct explanation of (A). \[ \boxed{\text{Both (A) and (R) are true and (R) is the correct explanation of (A).}} \]