Assuming $1 \mu \mathrm{~g}$ of trace radioactive element X with a half life of 30 years is absorbed by a growing tree.
The amount of X remaining in the tree after 100 years is $\_\_\_\_$ $\times 10^{-1} \mu \mathrm{~g}$.
[Given : $\ln 10=2.303 ; \log 2=0.30$ ]
