a) black tile
You can observe that column 7 it’s all alternating black tiles, what is different is the row numbers. Interestingly if you observe the even row numbers (2,4,6, etc) it is black tile. Odd row numbers are white tiles. So since 50 is an even number, the pattern follows a black tile

b) white tile
using the column pattern: 3,7, 11,15,19,23,37, 31, 35, etc.
We find column 31 in this list. So the pattens is that of part a, where we look at row numbers to determine the colour. Since row 1(odd)= white

C) total number of tiles = 100x100 = 10,000
Use pattern 6x6 in diagram as a guide. We can count that there are altogether 18 white tiles in (6x6)=36 tiles. Therefore, in column 100 and row 100, There are half the number of white tiles. 10,000/2 = 5000

Hope my explanations above is clear. I used observation and some simple pattern to find the answers.