What is the atomic mass of element X if 10.69 g XCl3 contains 5.55 g X?

Atomic mass of element X = 115 g/mol (Approx)

Explanation:

Given:

Amount of XCl3 = 10.69 gram

Amount of X = 5.55 gram

Find:

Atomic mass of element X

Computation:

Moles of Cl =  [Mass of Cl / Molar mass of Cl )

Moles of Cl = [(10.69 - 5.55 ) / 35.5]

Moles of Cl = 0.14479 (Approx)

Moles of X = 0.14479 / 3

Moles of X = 0.04826

Atomic mass of element X = 5.55 / 0.04826

Atomic mass of element X = 115 g/mol (Approx)

it's c. elements are placed in rows based on how may valencies electrons have.