rick007chakrabortyg10:
if I buy a new arduino which safety I have to maintain during experiments and by the way can I know your name please if you are agree to tell me
Do not apply a voltage higher than Vcc (5v on Uno, 3.3v on some other boards, see board docs) or lower than ground to any pin. Do not attempt to power motors or other large inductive loads off the 5v from the Arduino - these need a separate power supply. Do not connect an external voltage to the 5v pin when Arduino is plugged into USB (to use a 5v external power supply, use the USB connector - you can use phone chargers and USB cable to power it, and by using the USB connector to supply the power, you are physically prevented from connecting it to USB while it's connected to the external supply). Use the barrel jack if using an external power supply of 6.5v ~12v (note that lower voltages are better for external supply via barrel jack - lets you draw more current without overheating the regulator). Do not apply any external voltage to any pin when the board is not powered. Make sure that your workspace is free of conductive debris.
Also, please read How to use this forum - please read - Website and Forum - Arduino Forum; do not hijack unrelated threads.
There is no reason for us to give you our name. We are volunteers with no affiliation to Arduino other than being active users of it - all of our advise is dispensed without any guarantee!