4.5g mass of a substance (molar mass = 90g/mol) is dissolved in 250ml solution, the molarity of solution is

Answer

To find the molarity of the solution, we can follow these steps:

### Step 1: Calculate the number of moles of the solute.
The formula to calculate the number of moles is:

\[ \text{Number of moles} = \frac{\text{mass of solute (g)}}{\text{molar mass (g/mol)}} \]

Given:
- Mass of the substance = 4.5 g
- Molar mass = 90 g/mol

Substituting the values:

\[ \text{Number of moles} = \frac{4.5 \, \text{g}}{90 \, \text{g/mol}} = 0.05 \, \text{moles} \]

### Step 2: Convert the volume of the solution from milliliters to liters.
Since molarity is defined as moles per liter, we need to convert the volume from milliliters to liters.

Given:
- Volume of solution = 250 ml

To convert ml to liters, we use the conversion factor:

\[ \text{Volume in liters} = \frac{250 \, \text{ml}}{1000} = 0.25 \, \text{liters} \]

### Step 3: Calculate the molarity of the solution.
The formula for molarity (M) is:

\[ \text{Molarity (M)} = \frac{\text{Number of moles of solute}}{\text{Volume of solution in liters}} \]

Substituting the values:

\[ \text{Molarity} = \frac{0.05 \, \text{moles}}{0.25 \, \text{liters}} = 0.2 \, \text{M} \]

### Final Answer:
The molarity of the solution is **0.2 M**.

---