100 is even, divide by 2 =50
50 is even, divide by 2 = 25
25 is odd, so multiply by 3 and add 1 → 76
76 is even, divide by 2 = 38
38 is even, divide by 2 = 19
19 is odd, so multiply by 3 and add 1 → 58
58 is even, divide by 2 = 29
29 is odd, so multiply by 3 and add 1 → 88
88 is even, divide by 2 = 44
44 is even, divide by 2 = 22
22 is even, divide by 2 = 11
11 is odd, so multiply by 3 and add 1 → 34
34 is even, divide by 2 = 17
17 is odd, so multiply by 3 and add 1 → 52
52 is even, divide by 2 = 26
26 is even, divide by 2 = 13
13 is odd, so multiply by 3 and add 1 → 40
40 is even, divide by 2 = 20
20 is even, divide by 2 = 10
10 is even, divide by 2 = 5
5 is odd, so multiply by 3 and add 1 → 16
16 is even, divide by 2 = 8
8 is even, divide by 2 = 4
4 is even, divide by 2 = 2
2 is even, divide by 2 = 1
Yes, the Collatz conjecture holds for the starting number 100.