Fill in the blank with the correct choice given in the bracket - Dry hydrogen chloride gas can be collected by …………… displacement of air. [downward/upward]

State one relevant observation - Lead nitrate solution is mixed with dilute hydrochloric acid and heated.

Write a balanced chemical equation for - Action of dilute hydrochloric acid on magnesium sulphite.

Name the acid used for the preparation of - hydrogen chloride gas in the laboratory. State why this particular acid is preferred to other acids.