Which of the following is not a correct statement

Options

A. Resistivity of electrolytes decreases on increasing temperature
B. Resistance of mercury falls on decreasing its temperature
C. When joined in series a 40 W bulb glows more than a 60 W bulb
D. Resistance of 40 W bulb is less than the resistance of 60 W bulb

Explanation

To determine which statement is not correct, we will analyze each option one by one.

### Step 1: Analyze Option 1
**Statement:** The resistivity of electrolytes decreases on increasing temperature.

**Explanation:** This statement is true. As temperature increases, the movement of ions in the electrolyte becomes more vigorous, leading to increased conductivity and decreased resistivity.

### Step 2: Analyze Option 2
**Statement:** The resistance of mercury falls on decreasing its temperature.

**Explanation:** This statement is also true. Mercury is a good conductor, and its resistance decreases when the temperature decreases. This is a characteristic behavior of conductors.

### Step 3: Analyze Option 3
**Statement:** When joined in series, a 40 watt bulb glows more than a 60 watt bulb.

**Explanation:** This statement is true. In a series circuit, the current is the same through both bulbs. The brightness of a bulb is inversely proportional to its rated power. Therefore, the 40 watt bulb will glow brighter than the 60 watt bulb because it has a lower power rating.

### Step 4: Analyze Option 4
**Statement:** The resistance of a 40 watt bulb is less than the resistance of a 60 watt bulb.

**Explanation:** This statement is false. The resistance of a bulb is inversely proportional to its power rating when the voltage is constant. Since the 60 watt bulb has a higher power rating, it will have a lower resistance compared to the 40 watt bulb. Therefore, this statement is incorrect.

### Step 5: Analyze Option 5
**Statement:** The resistance of electrolytes decreases on increasing temperature.

**Explanation:** This statement is true. Similar to Option 1, as temperature increases, the mobility of ions increases, leading to decreased resistance.

### Conclusion
After analyzing all the options, we find that **Option 4** is the incorrect statement.

### Final Answer
The statement that is not correct is **Option 4**: The resistance of a 40 watt bulb is less than the resistance of a 60 watt bulb.

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