The "gas" that was used in ww i contained phosgene. into what corrosive chemical was this gas changed when it met with the moisture in the lungs

HCl

Explanation:

Phosgene (COCl₂) on reaction with moisture in lungs converts into Carbon dioxide and hydrochloric acid.

COCl₂ + 2 H₂O → CO₂ + 2 HCl

The HCl produced in lungs causes problems. It reacts with alveoli proteins resulting in suffocation, coughing, eyes and throat irritation and difficulty in breathing.