This is an acid-base reaction (neutralization): Ca(OH)2 is a base, HNO3 is an acid.
Reactants:
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Ca(OH)2 – Calcium hydroxide
Other names: {{ubl, Slaked lime, Calcium hydrate
Appearance: White powder ; Colourless crystals or white powder ; White, odorless powder. [Note: Readily absorbs CO2 from the air to form calcium carbonate.]
HNO3 – Nitric acid
Other names: Aqua fortis, Spirit of niter, Eau forte
Appearance: Colorless, yellow or red fuming liquid ; Colourless-to-yellow liquid with pungent odour ; Colorless, yellow, or red, fuming liquid with an acrid, suffocating odor. [Note: Often used in an aqueous solution. Fuming nitric acid is concentrated nitric acid that contains dissolved nitrogen dioxide.]