Why is copper (i) sulfate cu2so4^-2? not copper (ii)?

This is because Copper (I) has +1 charge and Copper (II) has +2 charge.

The chemical formula of an ionic compound consists of cation first, followed by anion. Both cations and anions are incolved to make compound to be nutral or charge entity for example Cu2SO4 is cuprous compound contain Cu (I) where two Cu give only one electron as  

Cu is cation and SO4 is anion

SO4 has a valency of -2

So, Cu2 has a valency of +2

But in Cu (II), The single copper gives two electron to SO4 and form CuSO4 compound named as copper sulphate.

These metalls are called transition metals who can change their oxidation states

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.

the answer is barium and copper bromide