Rust is formed by the interaction of iron and oxygen. when rust formed on an iron nail with a mass of 100 g, the mass of the rusted nail was 143 g. what mass of oxygen gas most likely reacted with the iron nail? 43 g 50 g 100 g 243 g

43 grams.

This problem is a good example to understand  the law of conservation of mass. This law states that mass can neither be created nor destroyed , meaning that the final mass is the same that what you started with..

You didn't measure the weight of the oxygen that entered the reaction, so the weight of the rustic nail, plus the weight of the oxygen, will be the equal to the final mass. 

100 +43 = 143g 

he would use the colour black