This question tests four important reactions from the Aldehydes, Ketones and Carboxylic Acids chapter. (i) is Friedel-Crafts alkylation where benzene reacts with ethyl chloride in presence of anhydrous AlCl₃ to give ethylbenzene. (ii) involves organocadmium reagents which are less reactive than Grignard reagents and react selectively with acid chlorides to give ketones. (iii) is Kucherov's reaction - hydration of alkynes catalyzed by Hg²⁺ gives ketones following Markovnikov's rule. (iv) is Etard reaction where chromyl chloride selectively oxidizes methyl group of toluene to aldehyde.