According to the universally accepted IUPAC "Golden Rule" for constructing a correct and standard 2D — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

The strict IUPAC standard (often termed the Golden Rule) for drawing valid Fischer projections mandates that the main parent carbon backbone is oriented vertically along the page. Furthermore, the numbering dictates that the most highly oxidized carbon atom (for example, a $-CHO$ or $-COOH$ group) is placed at the absolute top (or as close to the top as structurally possible).