What property of hydrogen chloride is demonstrated when it is collected by downward delivery [upward displacement]. Why is hydrogen chloride not collected over water.

Of the two gases, NH₃ and HCl, which is more dense. Name the method of collection of this gas.

Give one example of a reaction between the above two gases which produces a solid.

Write equations for the reaction of dil. HCl with each of the following :

(i) iron

(ii) sodium hydrogen carbonate

(iii) iron [II] sulphide

(iv) sodium sulphite