National Technology Day is observed on 11 May. This day is celebrated annually to commemorate the successful underground nuclear test conducted by India in 1998. It marks the significant advancements made by Indian scientists and engineers in the field of technology and science.

Option 1 is incorrect because 9 August is not the correct date for National Technology Day. Option 2 is also incorrect as 8 September is not the observed date for this day. Option 4 is also not correct as 17 May is not the designated date for the observance of National Technology Day.

Therefore, the correct answer is option 3, 11 May. This date holds historical significance as it represents the day on which India demonstrated its capability in nuclear technology and asserted itself as a pioneering technological nation.