Option 1 -> National Product refers to the total value of goods and services produced, not a price ratio.
Option 2 -> Wholesale Price Index measures price changes at wholesale level, not GDP ratio.
Option 3 -> Consumer Price Index measures price changes in consumer goods basket, not GDP ratio.
Option 4 -> GDP deflator is calculated as (Nominal GDP/Real GDP) × 100.
Hence, Option 4: GDP deflator -> The GDP deflator is precisely the ratio of nominal GDP to real GDP, multiplied by 100. It measures the change in prices of all goods and services included in GDP. Nominal GDP reflects current market prices, while Real GDP is adjusted for inflation using base year prices. Their ratio gives us the GDP deflator, which serves as a comprehensive measure of inflation across the entire economy, unlike CPI (which covers only consumer goods) or WPI (which covers only wholesale goods). -> correct