Option 1 states that both the Assertion (A) and Reason (R) are true, and that R is the correct explanation of A. This means that the first living organisms evolved on Earth were Chemo-heterotrophs and the reason for this is because at that time, there was no molecular oxygen.

Option 2 states that both the Assertion (A) and Reason (R) are true, but R is not a correct explanation of A. This means that while the first living organisms evolved on Earth were Chemo-heterotrophs, the absence of molecular oxygen is not the reason for this.

Option 3 states that A is true, but R is false. This means that the first living organisms evolved on Earth were Chemo-heterotrophs, but the reason for this is not because of the absence of molecular oxygen.

Option 4 states that A is false, but R is true. This means that the first living organisms evolved on Earth were not Chemo-heterotrophs, but it is true that there was no molecular oxygen at that time.

Based on the provided information, the correct answer is option 2, where both A and R are true but R is not a correct explanation of A.