Identify the salt Q from the observation
Salt Q is white in colour. On strong heating, it produces buff yellow residue and liberates reddish brown gas. Solution of salt Q produces chalky white insoluble precipitate with excess of ammonium hydroxide.

Explanation

The salt Q is lead nitrate
`underset("(Q)")(underset("Lead nitrate Colourless")(2Pb(NO_(3))_(2)(s))) overset("heat")to underset("Lead monoxide Yellow")(2PbO(s))+ underset("Nitrogen dioxide Reddish brown")(4NO_(2(g))) + underset("Oxygen")(O_(2)(g))`
When reacted with ammonium hydroxide solution it gives a chalky white precipitate of lead hydroxide :
`underset("(Q)")(Pb(NO_(3))_(2))+2NH_(4)OH to 2NH_(4)NO_(3)+underset("chalky white ppt.")(Pb(OH)_(2))darr`