This is an acid-base reaction (neutralization): NH4Cl is an acid, NaOH is a base.
Reactants:
NH4Cl – Ammonium chloride
Other names: Sal ammoniac, Salmiac, Nushadir saltSal armagnac, Salt armoniack, Salmiak, Ammonium chloride fume, Amchlor, Ammoneric, Ammonium muriate, Darammon, Sal ammonia, Salammonite, [NH4]Cl, NH4Cl, Ammoniumchlorid, Azanium chloride, Ammonium muriate fume, Sal ammoniac fume
Appearance: White solid, hygroscopic ; Odourless colourless-to-white hygroscopic solid in various forms ; Finely divided, odorless, white particulate dispersed in air.
Appearance: White, waxy, opaque crystals ; White hygroscopic solid in various forms ; Colorless to white, odorless solid (flakes, beads, granular form).