Option 1: Rs. 90 per year -> This incorrectly deducts only Rs 10 from the total output.
Option 2: Rs. 100 per year -> This is the total value of output without any deductions.
Option 3: Rs. 70 per year -> This is the Net Value Added (after deducting both intermediate goods and depreciation).
Option 4: Rs. 80 per year -> This correctly calculates Gross Value Added.
Hence, Option 4: Rs. 80 per year -> Gross Value Added (GVA) = Value of Output - Value of Intermediate Consumption. GVA = Rs 100 - Rs 20 = Rs 80. Note that capital consumption (depreciation) of Rs 10 is NOT deducted when calculating GROSS value added. It would only be deducted to find Net Value Added (Rs 80 - Rs 10 = Rs 70). -> correct