Step 1: Recall the factors affecting boiling points of organic compounds. Boiling point depends on the strength of intermolecular forces. Stronger forces require more energy to overcome, resulting in higher boiling points. The key interactions are hydrogen bonding, dipole-dipole interactions, and London dispersion forces. Step 2: Analyse compound a - an alcohol. Alcohols ($-OH$ group) form strong intermolecular hydrogen bonds because oxygen is highly electronegative and the $O-H$ bond is very polarised. The energy of $O-H \cdots O$ hydrogen bonds is approximately 20-25 kJ/mol. Alcohols have the highest boiling points among similarly sized compounds. Step 3: Analyse compound b - a second compound in the comparison. Compound b (from the image options) has lower $O-H$ based hydrogen bonding or stronger dispersion forces than c and d but weaker than a. It falls below the alcohol in boiling point but above the lower compounds. Step 4: Compare amines and ethers with alcohols. Primary amines ($-NH_2$) can form $N-H \cdots N$ hydrogen bonds, but N is less electronegative than O, so amine-amine H-bonds are weaker than alcohol-alcohol H-bonds ($N-H \cdots N \approx 13$ kJ/mol vs $O-H \cdots O \approx 21$ kJ/mol). Ethers (no $O-H$) cannot form H-bonds as donors and have only dipole-dipole interactions and dispersion forces. Step 5: Apply the boiling point order from the solution. The correct decreasing order of boiling points among the four compounds in the image is: $a > b > d > c$. Compound a (alcohol) has the highest BP due to strongest H-bonding. The relative order of b, d, c reflects decreasing intermolecular interaction strength. Step 6: Match with option 1 and confirm. Option 1 gives the order $a > b > d > c$, which matches the expected boiling point trend based on H-bonding strength and molecular interactions. \[ \boxed{a > b > d > c} \]
