**Core Concept**
The initial decay rate of a radioactive substance is determined by the disintegration constant (A,) and the initial number of radioactive atoms (N0). The disintegration constant is a measure of the rate at which radioactive atoms decay per unit time.

**Why the Correct Answer is Right**
The initial decay rate (R0) can be calculated using the formula R0 = A_ * N0. Given that A_ = 0.01/sec and N0 = 6 x 10^23, we can substitute these values into the formula to get R0 = 0.01/sec * 6 x 10^23 = 6 x 10^21 Bq (becquerels). Since 1 Bq = 1 decay/sec, the initial decay rate is 6 x 10^21 decays/sec.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect because it does not account for the initial number of radioactive atoms (N0) in the calculation.

**Option B:** This option may be a distractor, but without the correct calculation, it is difficult to determine its accuracy.

**Option C:** This option is incorrect because it does not include the disintegration constant (A_) in the calculation.

**Clinical Pearl / High-Yield Fact**
The disintegration constant (A_) is a fundamental concept in nuclear physics and is used to describe the rate of radioactive decay. It is an important parameter in determining the half-life of a radioactive substance.

**Correct Answer:** 6 x 10^21.