In which step does a mistake first occur? 8 + 2 + (3 X 3 -2)
Step 1: 8 +2 + (3 x 1)
Step 2: 8 +2 + 3
Step 3: 4 + 3
Step 4: 7

Step 2 because they didn't multiply 3×3

0.02

step-by-step explanation:

time of 9 192 631 770 periods of the radiation corresponding to the transition between the 2 hyperfine levels of the ground state of the caesium 133 atom at 0 k (but other seconds are sometimes used in astronomy)