Sodium chloride solution also called normal saline solution which is safe to inject intravenously has a concentration of:

\(= 0.9\%\, \ (m/v)\)

The correct answer is option 1. \(= 0.9\%\, \ (m/v)\).

Let us look into the details of the normal saline solution and its concentration.

Normal saline solution, also known as physiological saline or isotonic saline, is a solution of sodium chloride (NaCl) in water. It is called "normal" because its osmolarity is similar to that of blood plasma, making it compatible with the human body and suitable for medical applications such as intravenous administration.

The concentration of a solution is typically expressed as a percentage by mass/volume (% m/v), which indicates the mass of solute (in this case, NaCl) dissolved in a given volume of solution (in this case, water).

For normal saline solution, the concentration is 0.9% (m/v) NaCl. This means that for every 100 mL of solution, there are 0.9 grams of NaCl dissolved in it.

Now, let's address each option:

1. \(= 0.9\%\, \ (m/v)\): This option states that the concentration of the normal saline solution is exactly 0.9% (m/v), which is correct. It accurately represents the typical concentration of normal saline solution used in medical practice.

2. \(> 0.9\%\, \ (m/v)\): This option suggests that the concentration of the normal saline solution is greater than 0.9% (m/v), which is incorrect. Normal saline solution is specifically defined as having a concentration of 0.9% (m/v) NaCl.

3. \(< 0.9\%\, \ (m/v)\): This option implies that the concentration of normal saline solution is less than 0.9% (m/v), which is also incorrect. Normal saline solution is defined by its concentration of 0.9% (m/v) NaCl.

4. \(> 0.9\%\, \ (m/v)\):  This option is a repetition of the second option and is also incorrect for the same reasons mentioned earlier.

In summary, the correct concentration of normal saline solution is \(= 0.9\%\, \ (m/v)\), as stated in option 1. This concentration is essential for ensuring isotonicity and compatibility with biological systems when used for medical purposes.