In human physiology, the normal total salt (sodium chloride and other salts) content in blood plasma is approximately within which of the following percentage ranges by weight?

Introduction:
Blood plasma is a complex fluid containing water, salts, proteins, nutrients and waste products. The concentration of salts, especially sodium chloride and other electrolytes, is carefully regulated to maintain osmotic balance and proper functioning of cells. This question asks you to recall the approximate percentage of total salts present in blood, a value often used to explain isotonic solutions and physiological saline.

Given Data / Assumptions:
- The question refers to total salt content in blood, mainly sodium chloride and other ions. - The answer choices include 1.85 to 1.9%, 11.85 to 11.9%, 2.85 to 2.9% and 0.85 to 0.9%. - We assume values close to those used for physiological saline solution. - The percentage is by weight in an approximate range, not an exact constant.

Concept / Approach:
Physiological saline solution used in medicine is typically 0.85% to 0.9% sodium chloride in water, designed to match the osmotic concentration of blood plasma. Total salts in blood, including sodium, potassium, chloride, bicarbonate and others, are close to this range. Values like 11% or 2.8% would represent much more concentrated salt solutions than what is present in human plasma and would likely be harmful. Therefore, the correct approximate range for total salt content in blood is 0.85 to 0.9% by weight.

Step-by-Step Solution:
Step 1: Recall that isotonic saline solutions for injections are about 0.85% to 0.9% sodium chloride. Step 2: Understand that these solutions are formulated to have the same osmotic concentration as blood plasma, preventing red blood cell shrinkage or swelling. Step 3: Recognise that the total salt concentration in blood is therefore close to this percentage range. Step 4: Compare the options and note that 11.85% is extremely concentrated and 2.85% is still about three times higher than normal plasma salt levels. Step 5: Choose 0.85 to 0.9% as the range that matches the physiological saline concentration used clinically.

Verification / Alternative check:
Physiology textbooks mention that 0.9% sodium chloride solution is isotonic with human blood and is widely used as normal saline. Tables of plasma composition show sodium concentrations around 135 to 145 milliequivalents per litre, which correspond to approximately 0.9% salt by weight in water. Although additional ions contribute slightly, the total salt content remains in the same approximate range. These sources reinforce that 0.85 to 0.9% is the correct answer.

Why Other Options Are Wrong:
1.85 to 1.9%: Almost double the physiological concentration; such a solution would be hypertonic and cause cells to lose water. 11.85 to 11.9%: Far too concentrated to be compatible with life; such high salt levels would be extremely damaging. 2.85 to 2.9%: Still significantly hypertonic compared to normal plasma, used rarely for specific treatments but not as a representation of normal blood salt content.

Common Pitfalls:
Students sometimes confuse the concentration of saline used for decongestant nasal drops or other specialised solutions with the standard physiological saline. Another trap is to choose the largest number, thinking that blood is very rich in salts, when in fact it is mostly water with relatively small amounts of dissolved substances. A reliable memory aid is that normal saline is close to 0.9%, which aligns with the true salt content of human plasma.

Final Answer:
The total salt content in human blood is approximately 0.85 to 0.9% by weight.