How would you identify substances in a question

Amass of 100.0 g of solute is dissolved in water so that 850. ml of a 0.7500 m solution has been prepared. what is the molar mass of the solute?

Use the half-reactions of the reaction au(oh)3 + hi -> au +i2 +h2o to answer the questions

)in the deacon process for the manufacture of chlorine, hcl and o2 react to form cl2 and h2o. sufficient air (21 mole% o2, 79% n2) is fed to provide 35% excess oxygen, and the fractional conversion of hcl is 85%. calculate the mole fractions of the product stream components.