what is the no in the unit place in 623 raised to the power 39 Please tell me

623³⁹

It is the last digit of the base which decides the units place digit of the number. Since, the last digit of the number is 3 and the cyclicity of 3 is 4, so we find (59/4) which gives a remainder of 3. So the unit digit of 623³⁹ will be the same as the last digit of 3³, i.e. 7.