An alkaline solution is used to reduce the concentration of carbon dioxide in a stream from 10% to 0.1% by absorption with irreversible chemical reaction. The overall number of transfer units based on gas phase is

ANS:B - 4.605

The overall number of transfer units (NTU) is a measure of the effectiveness of a mass transfer operation, such as absorption. It quantifies the degree of separation achieved between the two phases involved in the process. For absorption processes with irreversible chemical reactions, the overall NTU can be calculated using the equation: 𝑁𝑇𝑈=𝑉𝐺𝐾𝐿⋅𝑎NTU=KL​⋅aVG​​ Where:

• 𝑉𝐺VG​ = Gas flow rate at standard conditions
• 𝐾𝐿KL​ = Overall mass transfer coefficient
• 𝑎a = Specific interfacial area

Given the problem statement, we're asked to calculate the overall NTU based on the gas phase. The information provided includes the initial concentration of carbon dioxide (CO2) in the gas stream (10%) and the final concentration after absorption (0.1%). This change in concentration represents the degree of separation achieved. However, without the values for 𝑉𝐺VG​, 𝐾𝐿KL​, and 𝑎a, it's not possible to directly calculate the overall NTU. If the values for 𝑉𝐺VG​, 𝐾𝐿KL​, and 𝑎a were provided, we could plug them into the equation to find the overall NTU. Otherwise, it's not feasible to determine the exact value of NTU based solely on the information given. So, in this case, we can't calculate the overall NTU without additional information. Therefore, none of the provided options seem applicable without the necessary parameters.