The number of distinct prime factors of the largest 6-digit number is

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The correct option is 5.

To find the number of distinct prime factors of the largest 6-digit number, we start by determining the largest 6-digit number, which is 999999.

Now, we perform the prime factorization of 999999 step-by-step:

$999999=9\times 111111$

We break down each component further:

$9=3^2$

$111111=111\times 1001$

$111=3\times 37$

$1001=7\times 11\times 13$

Combining all the prime factors together:

$999999=3^3\times 7\times 11\times 13\times 37$

The distinct prime factors of 999999 are 3, 7, 11, 13, and 37.

Therefore, the number of distinct prime factors is 5.