See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Concept: The basic strength of halide ions is inversely related to the stability of their conjugate acids (the hydrohalic acids HX). A stronger acid has a weaker conjugate base, and vice versa. Step 1: Recall the acid strength order of hydrohalic acids. The acid strength increases down the group because the H-X bond becomes weaker (longer and less strong) as the size of X increases. Thus: HF << HCl < HBr < HI. HF is the weakest acid among the hydrohalic acids (it does not fully dissociate in water), while HI is the strongest. Step 2: Since basic strength of the conjugate base is inversely proportional to the acid strength of the conjugate acid, the basic strength order of halide ions is the reverse of the acid strength order of HX: F- > Cl- > Br- > I- F- is the strongest base because HF is the weakest acid (F- has the greatest tendency to accept a proton back). I- is the weakest base because HI is the strongest acid. Step 3: Evaluate the options. (a) F- > Cl- > I- > Br- — incorrect order (Br- and I- are swapped) (b) F- > Cl- > Br- > I- — matches the correct decreasing basic strength order (c) I- > Br- > Cl- > F- — this is the order of increasing basic strength (i.e., nucleophilicity in polar aprotic solvents or polarizability), not decreasing basic strength in the Bronsted sense (d) I- > Cl- > Br- > F- — incorrect order Why other options fail: Options (c) and (d) reverse the correct trend; option (a) incorrectly places I- before Br-. Therefore, the correct answer is B.