What is the ratio of nv/n (1357 k) and nv/n (298k)?

Ratio is a way of comparing two numbers which are of the same kind. It is normally expressed by separating two numbers with a colon(:) or you could also use division sign (/). The only way that ratios can have mean is that both number should be non-zeros and both of them should have the same sign. Thus having this in mind, the ratio of the numbers above will be:
(1357k)/(298k)
=1357:298

We have two constant for calculating Nv/N values of temperature, Assuming the Energy for vacancy formation Qv = 0.90 eV/atom Temperature contant K = 8.62 x 10^-5 eV Calculating for temperature 1357 k Nv / N (1357 k) = exp (Qv / kT) = exp (0.90 / (8.62 x 10^-5 x 1357)) = 4.56 x 10^-4 Calculating for temperature 298 k Nv / N (298 k) = exp (Qv / kT) = exp (0.90 / (8.62 x 10^-5 x 298)) = 6.08 x 10^-16 Finally calculating the ratio, Nv / N (1357 k) / Nv / N (298 k) = 4.56 x 10^-4 / 6.08 x 10^-16 Nv / N (1357 k) / Nv / N (298 k) = (4.56 / 6.08) x 10^12 = 75 x 10^10 So the ratio is 75 x 10^10.