When carbohydrates are used as substrate and are completely oxidised, the RQ will be : 

One

The correct answer is Option (3) –One

RESPIRATORY QUOTIENT :

During aerobic respiration, O₂ is consumed and CO₂ is released. The ratio of the volume of CO₂ evolved to the volume of O₂ consumed in respiration is called the respiratory quotient (RQ) or respiratory ratio.

The respiratory quotient depends upon the type of respiratory substrate used during respiration. When carbohydrates are used as substrate and are completely oxidised, the RQ will be 1, because equal amounts of CO₂ and O₂ are evolved and consumed, respectively.

When fats are used in respiration, the RQ is less than 1.

When proteins are respiratory substrates the ratio would be about 0.9. What is important to recognise is that in living organisms respiratory substrates are often more than one; pure proteins or fats are never used as respiratory substrates.