Which describes a chemical property of silicon? (1) silicon has a blue-gray color
(2) silicon is a brittle solid at 20oc
(3) silicon melts at 1414oc
(4) silicon reacts with fluorine

The answer is (4) Silicon reacts with fluorine. The other three are just physical properties and are intensive (properties do not change, such as melting point, freezing point, color, etc.)
Hope this would work:)) 

The answer is 3,5g co