Name some aquatic habitats?

Explanation

Chemistry of Lassaigne.s test for detection of nitrogen : During the detection of nitrogen, a few drops of dil. NaOH are added into the lassaigne.s extract. To a part of this alkaline solution, a few drops of freshly prepared ferrous sulphate are added. Then it is warmed, a little cooled and few drops of ferric chloride solution are added to it, then acidified with dil. `H_2SO_4` Appearance of green or blue colouration indicates the presence of nitrogen.
`underset("From organic compound")(Na + C + N) overset(Delta)(rarr)NaCN`
`2NaCN + FeSO_4 to Na_2SO_4 + underset("Ferrous cyanide")(Fe(CN)_2)`
`Fe(CN)_2 + 4 NaCN to underset("Sodium ferrocyanide")(Na [Fe(CN)_6])`
`3Na_4[Fe(CN)_6]+4Fe^(+3) to underset("(blue colour)")underset("Ferric ferrocyanide")(Fe_4[Fe(CN)_6]_3 + 12Na^(+))`