Sulfur trioxide decomposes to sulfur dioxide and oxygen gas as shown in the following reaction:
2503 (g) 2502 (g) + O2 (g)
Given a 240.0 g sample of sulfur trioxide (MM = 80.1 g/mol),
how many grams of oxygen (MM = 32.0 g/mol) are
produced, assuming the decomposition goes to
completion?

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

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.  

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.