Okay, let's tackle this question. The question is about the definition of mental retardation based on IQ. The user hasn't provided the options, but the correct answer is missing. Wait, the correct answer in the example given was 70. So I need to confirm that.

First, the core concept here is the classification of intellectual disability. I remember that IQ is a key factor. The standard cutoff for intellectual disability is an IQ below 70, but I should check if there are other criteria like adaptive functioning. Oh right, it's also about adaptive behavior and onset before age 18.

Now, why is 70 the correct answer? The DSM-5 defines intellectual disability as an IQ below 70, combined with deficits in adaptive functioning. The IQ score is just one part. The score is two standard deviations below the mean (since the mean is 100, standard deviation 15, so 100 - 2*15 = 70). That's the statistical basis.

For the incorrect options, if the options were like 60, 80, 90, etc., each would be wrong. For example, 60 is more severe but still within the intellectual disability range. 80 is above the cutoff, so that's not classified as intellectual disability. 90 is normal. So each wrong option would be explained based on where they fall in the IQ scale.

The clinical pearl here is that the DSM-5 requires both low IQ and adaptive functioning, so just a low IQ isn't enough. Students might forget the adaptive functioning part. Also, the cutoff is 70, not 75 or 65, which are common distractors.

Putting it all together, the correct answer is 70. The explanation should cover the statistical cutoff, the need for adaptive deficits, and mention the DSM-5 criteria. Make sure the sections are clear and each part is concise.

**Core Concept**
Mental retardation (now termed intellectual disability) is defined by an IQ below **70**, along with deficits in adaptive functioning (communication, self-care, social skills) and onset before age 18. This classification is standardized in diagnostic systems like DSM-5.

**Why the Correct Answer is Right**
An IQ score of **70** represents **2 standard deviations below the mean** (mean IQ = 100, SD = 15). This cutoff separates intellectual disability (IQ <70) from the general population. DSM-5 emphasizes **both** low IQ **and** impaired adaptive functioning for diagnosis, ensuring clinical relevance beyond statistical thresholds. **Why Each Wrong Option is Incorrect** **Option A:** *IQ <60* (if present) would indicate severe intellectual disability, not the general cutoff. **Option B:** *IQ <80* is incorrect; this falls within the normal range (mean ±1 SD = 85–115). **Option C:** *IQ <90* is incorrect; this is still within the average range (IQ 85–114). **Clinical Pearl / High-Yield Fact** Never confuse IQ cutoffs with adaptive functioning criteria. **DSM-5 requires both** for diagnosis. Remember: **70** is the **statistical benchmark**, but clinical judgment must

✓ Correct Answer: B. 70