Which is not correct ?

Options

A. (a) `Na^(+)` ions help retain water
B. (b) `Na^(+)` ions help conduct nerve impulse
C. (c) `Na^(+)`ions help in transport of substances across membranes
D. (d) NaCl is component of blood

Answer

To determine which statement is not correct regarding sodium ions (Na+), let's analyze each option step by step.

### Step 1: Analyze Option A
**Statement:** Sodium ions help retain water.
**Analysis:** Sodium ions do play a role in the retention of water in the body. They help regulate fluid balance and are involved in maintaining osmotic pressure. However, the statement may be misleading as it implies that sodium ions solely help in water retention without mentioning their role in retaining other body fluids. Thus, this statement is somewhat correct but not entirely accurate in its implication.

### Step 2: Analyze Option B
**Statement:** Sodium ions help conduct nerve impulses.
**Analysis:** This statement is correct. Sodium ions are critical for the generation and propagation of action potentials in neurons. The sodium-potassium pump maintains the concentration gradient necessary for nerve impulse conduction, making this statement true.

### Step 3: Analyze Option C
**Statement:** Sodium ions help in the transport of substances across membranes.
**Analysis:** This statement is also correct. Sodium ions are involved in various transport mechanisms, including the sodium-glucose symporter, which helps transport glucose across cell membranes. Therefore, this statement is accurate.

### Step 4: Analyze Option D
**Statement:** NaCl is a component of blood.
**Analysis:** This statement is correct. Sodium chloride (NaCl) is indeed a component of blood, particularly in blood plasma, where it helps maintain osmotic balance and fluid distribution. Thus, this statement is true.

### Conclusion
After analyzing all options, the statement that is not entirely correct is **Option A**, as it oversimplifies the role of sodium ions in water retention without acknowledging their broader physiological functions.

### Final Answer
**The statement that is not correct is Option A: Sodium ions help retain water.**

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