Match List - I with List - II.

List-I (Salt)	List-II (Flame colour wavelength)
(a) LiCl	(i) 455.5 nm
(b) NaCl	(ii) 670.8 nm
(c) RbCl	(iii) 780.0 nm
(d) CsCl	(iv) 589.2 nm

Choose the correct answer from the options given below:

Alkali metals and their salts produce characteristic flame colours when heated. The flame colour corresponds to specific wavelengths of light emitted when excited electrons return to lower energy levels. The key flame colours and their wavelengths for alkali metal chlorides are as follows.

Lithium chloride (LiCl) produces a crimson red flame, which corresponds to a wavelength of approximately $$670.8$$ nm. Sodium chloride (NaCl) produces the well-known intense yellow flame, corresponding to the sodium D-line at approximately $$589.2$$ nm. Rubidium chloride (RbCl) produces a red to red-violet flame at approximately $$780.0$$ nm (near the infrared boundary). Caesium chloride (CsCl) produces a blue-violet flame at approximately $$455.5$$ nm.

Matching the salts with their flame colour wavelengths: (a) LiCl matches with (ii) 670.8 nm, (b) NaCl matches with (iv) 589.2 nm, (c) RbCl matches with (iii) 780.0 nm, and (d) CsCl matches with (i) 455.5 nm.

Therefore, the correct answer is Option (4): (a)-(ii), (b)-(iv), (c)-(iii), (d)-(i).