an element E forms a hydride EH3, which contains 90% of E by mass. what is the relative atomic mass ?​

27 g/mol of E

Explanation:

Note that percentage by mass= mass of each element present. So, since there is 90% of E, there is 90g of E present. By implication, there are 10g of H corresponding to 10%H. Note that there is 100g of EH3

1 moles of E corresponds to 90 g of E

Mole ratio of E: H= 1:3

Thus

Number of moles of H = 10g/ 1g/ mol = 10 moles of H

Since E contains 1/3 the number of moles of H

Number of moles of E = 1/3 × 10 = 3.33 moles of E

Molar mass of E= mass of E/ number of moles of E

Since mass of E = 90 g

Molar mass of E = 90g/3.33 moles

Molar mass of E = 27 g/mol

every chemical equation adheres to the law of conservation of mass, which states that matter cannot be created or destroyed. therefore, there must be the same number of atoms of each element on each side of a chemical equation.