. Electron cuối cùng của hai nguyên tố X và Y có bốn số lượng tử như sau: X n = 4, ℓ = 2, mℓ = –1, ms = +½
Y n = 3, ℓ = 1, mℓ = –1, ms = –½

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)

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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.