Okay, let's tackle this question about the number of double bonds in arachidonic acid. First, I need to recall what arachidonic acid is. It's a polyunsaturated fatty acid, right? I remember that omega-3 and omega-6 fatty acids have multiple double bonds. Arachidonic acid is part of the omega-6 family.

Wait, the question is asking specifically about the number of double bonds. Let me think. Arachidonic acid has the chemical formula C20H32O2. The general formula for a saturated fatty acid is CnH2nO2. If it's unsaturated, each double bond reduces the number of hydrogen atoms by two. So, each double bond corresponds to a decrease of two hydrogens.

Arachidonic acid has 20 carbons. A saturated version would have 40 hydrogens (since 2n=40 for n=20). But arachidonic acid has 32 hydrogens. The difference is 8 hydrogens. Each double bond accounts for 2 hydrogens missing, so 8 divided by 2 is 4. Therefore, there are 4 double bonds.

Wait, but I should verify. Alternatively, I remember that arachidonic acid is 20:4 (omega-6), meaning 20 carbons and 4 double bonds. The omega-6 refers to the position of the first double bond, which is at the sixth carbon from the methyl end. So the number of double bonds is definitely 4.

Now, the options aren't listed, but the correct answer is 4. The possible incorrect options could be numbers like 2, 3, or 5. Let's think about why others are wrong. For example, option B might be 3, which is the number of double bonds in alpha-linolenic acid (omega-3). Option C could be 5, which is linolenic acid. Option D might be 2, like in oleic acid. So the correct answer is 4.

**Core Concept**
Arachidonic acid is a 20-carbon polyunsaturated omega-6 fatty acid. The number of double bonds determines its degree of unsaturation, which is critical for its role in eicosanoid synthesis and membrane fluidity.

**Why the Correct Answer is Right**
Arachidonic acid has the chemical formula **C₂₀H₃₂O₂**. A fully saturated 20-carbon fatty acid would have **40 hydrogen atoms** (2n formula). Each double bond reduces hydrogen by 2. The observed 32 hydrogens indicate **4 double bonds** (40 - 32 = 8 missing H → 8/2 = 4 double bonds). This aligns with its systematic name, **icosatetraenoic acid**, where "tetra-" denotes four double bonds.

**Why Each Wrong Option is Incorrect**
**Option A:** 2 double bonds — Incorrect. This describes saturated fatty acids like stearic acid or monounsaturated fats like oleic acid.
**Option B:** 3 double bonds — Incorrect. This matches alpha-linolenic acid (omega-3) or gamma-linolenic acid (omega-6), but not arach

✓ Correct Answer: D. 4