In standard form, the number 72105.4 is written as 7.21054 × 10ⁿ where n is equal to

For the standard form notation, only one number is kept before the decimal point and rest all numbers are written after decimal point.

The power of 10 denotes the number of terms shifted after the decimal point.

So for 72105.4,

Here only one number will be kept before decimal point that is 7.

Number of terms to be shifted after decimal point = 4

72105.4 = 7.21054 × 10⁴

So n = 4

So the correct answer is C.