There are 30 protons and 39 neutrons in the nucleus.
This must me the isotope of an element with an atomic mass close to 69 u.
The only candidates are Zn and Ga.
Zn has a zinc-69 isotope with mass 68.926 u.
Ga has a gallium -69 isotope with mass 68.925 u.
The isotope is probably

.
It has 30 protons and 39 neutrons.
CH4+ 2O2---> CO2+ 2H2O I believe would be correct.
Since the question says “these” I assume it was multiple choice...but anyways, intermolecular forces between some of the water molecules are breaking apart. The H2O is going from a tightly packed solid of a fixed volume to a liquid with molecules moving faster and less bonds, which can take the shape of its container. It requires energy to break a bond, so this is an endothermic process.
<span>The answer is (1) chemically combined in a fixed proportion. Elements in a compound are bound by a chemical bond. So, oxygen and hydrogen are bound chemically. Further, their proportion never changes, it is always 1 oxygen atom and 2 hydrogen atoms in water. Thus, elements in a compound are chemically combined in a fixed proportion.Hope this helps. Let me know if you need additional help!</span>