Answer:
chemistry - the science that studies the properties of substances and natural fenomens .
...........
Answer:
Explanation:
From the periodic table, the element designated as Sn is tin. Sn is derieved from a latin name of the metal called Stanum
Selenium Se is a group 6 element. It belongs to the same group with oxygen, sulfur and tellurium. This substance has an atomic weight of 78.96g/mol
Oxygen is a group 6 element with an atomic mass of 16. The atomic mass is the number of protons in the nucleus of this atom.
Answer:
A full moon occurs when the Moon appears as a complete circle in the sky.
Explanation:
- We see it as a full orb because the whole of the side of the Moon facing the Earth is lit up by the Sun's rays.
- The moon shows no visible light of its own, so we only see the parts of the moon that are lit up by other objects.
Answer:
A. there is an isotope of lanthanum with an atomic mass of 138.9
Explanation:
By knowing the different atomic masses of both Lanthanum atoms, we can not tell anything about their occurence in nature. Therefore, all the last three options are incorrect. Because, the atomic mass does not tell anything about the availability or natural abundance of an element.
Now, the isotopes of an element are those elements, which have same number of electrons and protons as the original element, but different number of neutrons. Therefore, they have same atomic number but, different atomic weight or atomic masses.
Hence, by looking at an elements having same atomic number, but different atomic masses, we can identify them as isotopes.
Thus, the correct option is:
<u>A. there is an isotope of lanthanum with an atomic mass of 138.9.</u>
