The largest \[8\] digit number is
A.\[888999\]
B.\[99999999\]
C.\[999999\]
D.\[8999999\]

Hint: In the given problem, we have to find out from the four given options which one is the largest \[8\]-digit number. We will find it or check it by taking all the four options one after another and hence, we will get the largest \[8\]-digit number.

Complete step-by-step answer:
The given question is about writing the largest eight-digit number.
First of all, the largest number is the number which is larger than all others. No another number is greater than that number. \[8\]-digit number is the number containing a total of eight digits. Now, we will check each given option one after another.
In the first option, we are given \[888999\] and we have to check that this is the largest \[8\]-digit number or not. Since, \[888999\] contains \[6\]-digit but we want \[8\]- digit largest number.
Therefore, option (A) is wrong.
In the second option, we are given \[99999999\] and we have to check that this is the largest \[8\]-digit number or not. Since \[99999999\] contains \[8\]-digits and also, this is the largest \[8\]-digit number. If we add \[1\] in \[99999999\], we get \[100000000\] which will become \[9\]-digit number.
Therefore, option (B) is correct.
In the third option, we are given \[999999\], which is \[6\]-digit number and hence, the third option is also incorrect.
In the last option, we are given \[8999999\]. Since, this number contains \[7\]-digits. Therefore, this option is also incorrect. This is not the largest \[8\]-digit number.
Therefore, option (B), \[99999999\] is the largest \[8\]-digit number.

Note: If we want to write the smallest \[8\]-digit number, it would contain \[8\] digits which are \[10000000\]. If we check this, subtract \[1\] from \[10000000\], we get \[9999999\], which is \[7\]-digit number. Hence, \[10000000\] is the smallest \[8\]-digit number. To check the greatest number, add \[1\] to it and to check the smallest number, subtract \[1\] from it, then check that the number of digits remains the same.