Astudent obtains a mixture of the chlorides of two unknown metals, x and z. the percent by mass of x and the percent by mass of z in the mixture is known. which of the following additional information is most in calculating the mole percent of xcl(s) and of zcl(s) in the mixture?

the Molar masses of Z and X

Explanation:

The percent by mass of X states how many grams of X are in 100 grams of the mixture. Then, we know how many grams of X, Z (we also know its percent) and of Cl ( = 100 - X % - Z %). Taking 100 g of the mixture as a base, we have:

x grams of X

z grams of Z

y grams of Cl

With the molar masses of Z and X (and of Cl) we can transform all masses into moles and then compute the mole percent of XCl(s) and of ZCl(s) in the mixture

that tool would be a compass