Choose the substance with the lowest vapor pressure at a given temperature.

(a) bf3
(b) pf5
(c) becl2
(d) he
(e) co2

C

Explanation:

The vapor pressure is the pressure that the vapor does when it is in equilibrium with the liquid that originated it. So, it's a measure of the tendency of the boil of the liquid, and as higher is the vapor pressure, more easily will be to the liquid to boils, so lower will be the boiling point.

The boiling point depends on the strength of the intermolecular force of the substance and the molar mass of the substance. As higher is them, as higher is the boiling point.

BF3 is a nonpolar covalent compound, so it has London forces, which are the weakest. It has 67.82 g/mol of molar mass.

PF5 is also a nonpolar covalent compound and has London forces. Its molecular mass is 126 g/mol.

BeCl2 is an ionic compound formed by the ions Be+2 and Cl-, and the ionic force (ion-ion) is the strongest. Its molar mass is 80 g/mol.

He is a noble has, and so, has a weak force between its atoms. Its molar mass is 4 g/mol.

CO2 is a nonpolar compound, so it has London forces too. It has a molar mass of 44 g/mol.

So, the compound of the strong molar force is BeCl2, and at room temperature, it is solid (all ionic compounds are solid at room temperature). All the other compounds are gases at room temperature, so BeCl2 has the highest boiling point, and because of that, the lowest vapor pressure.

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current

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.