Question

thermometer measure its own temperature .justify

Answer 1

When a thermometer is showing a steady reading, it is in thermal equilibrium with the thing it's measuring. So, as much heat flows into the thermo from the thing as flows out from the thermo into the thing. The thermo and the thing are thus at the same temperature. So, in that sense, the thermo is measuring its own temperature, and this temperature is the same as the temperature of the thing its measuring.