<u>Answer:</u> The Henry's law constant for oxygen gas in water is 
<u>Explanation:</u>
To calculate the molar solubility, we use the equation given by Henry's law, which is:

where,
 = Henry's constant = ?
 = Henry's constant = ?
 = solubility of oxygen gas =
 = solubility of oxygen gas = 
 = partial pressure of oxygen gas = 2.1 atm
 = partial pressure of oxygen gas = 2.1 atm
Putting values in above equation, we get:

Hence, the Henry's law constant for oxygen gas in water is 