chi square table in mathematica

You can do the integration with CFD and reverse with Quantile, e.g.

NIntegrate[PDF[ChiSquareDistribution[2], a], {a, 0, 3.0}]

0.77687

p = CDF[ChiSquareDistribution[2], 3.0]

0.77687

Quantile[ChiSquareDistribution[2], p]

Re. your link

Quantile[ChiSquareDistribution[2], 1 - #] & /@ {0.995, 0.975, 0.20, 0.10, 0.05};
SetPrecision[#, If[# < 1, 3, 4]] & /@ %

{0.0100, 0.0506, 3.219, 4.605, 5.991}