A. 4. Identify the ions in (NH4)2Cr2O7.
N3-, H+, Cr3+ and O2-
b. N3-, H., Cr3+ and O2-
NH4+ and Cr2O72-
d. NH3 and H2Cr2O7
e. NH4+, Cr3+ and 02-
c.
Identify the ions.

it means there are 3 atoms of oxygen

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.