None.
A square kilometre is a measure of area. It has no thickness and so no volume. It cannot, therefore contain any atoms.
The number of atoms in a cubic kilometre will depend on whether you are talking about interstellar space, the earth's atmosphere, ordinary matter, a stellar core or a black hole. The answer will range from nearly zero to infinity.
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1.75 sq. km
254,805 km2
Answer: 9,600,000 square km = 5,965,163.445 square miles
1 hectare = 0.01 square kilometers
China is between 9,596,961 to 9,639,688 sq. km.