Which of the following represents a double displacement reaction? MCQ with Answer and Explanation

Explanation:
Sulphuric acid is a key reagent in many processes: to produce HCl from NaCl, HNO₃ from nitre, fertilizers (superphosphate), and in petroleum refining, pickling, etc. It is also used as a dehydrating agent and catalyst. Ammonia is made by Haber process without H₂SO₄. NaOH is made by electrolysis of brine. H₂SO₄ is known as 'king of chemicals'.

Explanation:
Standard reduction potential (E°) measures the tendency of a species to gain electrons and be reduced. The more positive the E°, the greater the tendency to undergo reduction. Metals with negative E° are good reducing agents (e.g., Zn, -0.76 V). E°cell = E°cathode - E°anode. It is measured under standard conditions (1 M, 1 atm, 25°C) relative to standard hydrogen electrode (SHE) which is assigned 0 V.

Explanation:
Aluminium displaces iron from iron(III) oxide because Al is more reactive. This is a single displacement (or thermite) reaction. Also redox: Al oxidized, Fe reduced. Combination: one product; decomposition: one reactant.