What are the number of electrons and arrangement in each element?

In Ca F₂

Ca²⁺ has 18 electrons with

K Shell  2 electrons

L shell  8  electrons

M shell 8 electrons

N shell 2 electrons.

and

F⁻ has 10 electrons  with

K shell  2 electrons

L shell  8  electrons

In K₂S

Each K⁺ has 18 electrons with electronic arrangement

K shell  2 electrons

L shell  8  electrons

M shell 8 electrons

and S²⁻has 18 electrons with electronic arrangement

K shell  2 electrons

L shell  8  electrons

M shell 8 electrons

with 18 electrons.

Explanation:

CaF₂ is an ionic compound formed by a calcium ion and  2 flouride ions.

Atomic no. of Ca is 20.It has 20 protons in nucleus and 20 electrons.

Electronic arrangement:

K shell  2 electrons

L shell  8  electrons

M shell 8 electrons

N shell 2 electrons.

It loses 2 electrons of the valence N shell to get the  nearest noble gas configuration of Ar. SInce it loses 2 electrons it has two protons more than electrons and forms Ca⁺² ion.

F has atomic no. 9 .It has 9 protons in nucleus and 9 electrons.

Electronic arrangement:

K shell  2 electrons

L shell  7  electrons

It must gain 1 electron to get the nearest noble gas configuration(completely filled valence shell) of Ne.

2 F atoms take up one electron each that is lost by Ca to get an extra negative charge F⁻ and attain the noble gas configuration .Each Flourine atom now has 1 electron more than proton and becomes F⁻ ion.

So in Ca F₂

Ca²⁺ has 18 electrons with

K shell  2 electrons

L shell  8  electrons

M shell 8 electrons

N shell 2 electrons.

and

F⁻ has 10 electrons  with

K shell  2 electrons

L shell  8  electrons

K₂S is an ionic compound formed by 2 potassium ions and one sulfide  ion.

Atomic no. of K is 19.It has 19 protons in nucleus and 19 electrons.

Electronic arrangement:

K shell  2 electrons

L shell  8  electrons

M shell 8 electrons

N shell 1 electron

It loses 1 electron of the valence N shell to get the  nearest noble gas configuration of Ar.It loses 2 electrons of the valence N shell to get the  nearest noble gas configuration of Ar. SInce it loses one electron it has one proton more than electron and forms  K⁺ ion.In K₂S two such K⁺ ions are formed.

S has atomic no. 16 .It has 16 protons in nucleus and 16 electrons.

Electronic arrangement:

K shell  2 electrons

L shell  8  electrons

M shell 6 electrons

S atom take up 2 electrons that is lost by the two K atoms to get two extra negative charge S²⁻ and attain the noble gas configuration . Sulfur atom now has 2 electrons more than protons and becomes S²⁻ ion.

So in K₂S

Each K⁺ has 18 electrons with electronic arrangement

K shell  2 electrons

L shell  8  electrons

M shell 8 electrons

and S²⁻has 18 electrons with electronic arrangement

K shell  2 electrons

L shell  8  electrons

M shell 8 electrons

with 18 electrons.

the best answer is d because the strong cohesion is caused by the ability of water molecules to undergo hydrogen bonding.

a is incorrect because when water solidifies, it becomes   ice, which expands and occupies a bigger volume for the same mass of water in its liquid state.

b is incorrect because water has high surface tension. besides bonding to itself it hydrogen bonds to other molecules at the top decreasing possibility for breaking of attractive forces.

c is incorrect because the water molecule has oxygen which is highly electronegative and so pulls the electron pair towards itself creating a dipole moment, making the molecule polar.

e is incorrect because water has strong adhesion, ability to stick to other molecules such as glass because of this molecules having stronger hydrogen bonding than water.