Oxygen gas can be prepared by heating potassium chlorate according to the following equation: 17.2KClO3(s)2KCl(s) + 3O2(g)

The product gas, O2, is collected over water at a temperature of 25 °C and a pressure of 758 mm Hg. If the wet O2 gas formed occupies a volume of 9.07 L, the number of moles of KClO3 reacted was
mol. The vapor pressure of water is 23.8 mm Hg at 25 °C.

Moles KClO₃ = 0.239

Given

Reaction

2KClO₃(s) ⇒2KCl(s) + 3O₂(g)

P water = 23.8 mmHg

P tot = 758 mmHg

V = 9.07 L

T = 25 + 273 = 298 K

Required

moles of KClO₃

Solution

P tot = P O₂ + P water

P O₂ = P tot - P water

P O₂ = 758 - 23.8

P O₂ = 734.2 mmHg = 0.966 atm

moles O₂ :

n = PV/RT

n = 0.966 x 9.07 / 0.082 x 298

n = 0.358

From equation, mol ratio KClO₃ : O₂ = 2 : 3, so mol KClO₃ :

= 2/3 x mol O₂

= 2/3 x 0.358

= 0.239

assuming that your periodic table has eighteen columns, you should highlight   the four elements in the third column from the left of the table.

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the have energy higher than those in the orbital while lower than those of the orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the orbital is therefore filled right after orbitals and before orbitals.  

potassium has electron configuration and calcium . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the and should be highlighted as well.

it is the most commonly accepted one