Chemical formula for iron (l) selenide

Iron can not form iron(i) selenide however it can form iron(ii) selenide.

Explanation:

The possible oxidation states of iron are +2 and +3.

Iron can form iron (ii) selenide.

The formula of iron (ii) selenide is FeSe.

In iron (ii) selenide the oxidation state of iron is +2.

The ratio of both atoms are 1:1.

Its molecular weight is 134.82 g/mol.

It is toxic compound.

Its melting point is 965°C.

Its density is 4.72 g/cm³.

Iron can also form iron (iii) selenide.

The formula of iron (iii) selenide is Fe₂Se₃.

In  iron (iii) selenide the oxidation state of iron is +3.

The ration of both atoms are 2:3.

It also known as ferric selenide.

Its molecular weight is 348.57 g/mol.

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.