Anewly discovered element, y, has two naturally occurring isotopes. 87.8 percent of the sample is an isotope with a mass of 267.8 u, and 12.2 percent of the sample is an isotope with a mass of 269.9 u. what is the weighted average atomic mass for this element?

Answer : The average atomic mass of an element is, 268.6 amu.

Solution : Given,

Mass of isotope 1 = 267.8 amu

% abundance of isotope 1 = 87.8% = 0.878

Mass of isotope 2 = 269.9 amu

% abundance of isotope 2 = 12.2% = 0.122

Formula used for average atomic mass of an element :

Therefore, the average atomic mass of an element is, 268.6 amu.

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.