take example for such questions!....And then generalize
draw for 1 bit using (0 1) u will get a line shaped graph ...chromatic no. =2
draw for 2 bit using (00 01 10 11) u will get a square shaped graph......chromatic no. =2
draw for 3 bit using (000 001 010 011 100 101 110 111) u will get a 3-cube graph.....chromatic no. =2 ..
draw for 4 bit using (0000 0001......) u will get a 4-cube graph.....chromatic no. =2 ..
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hence for n bit u will get n-cube ...chromatic no. =2
Diameter is maximum length between any two vertices , Here its 5
So, ratio is 2/5