Not sure, but I would guess it's due to environmental factors, like heat, and imperfections in the metal. Just an educated guess, though.
Answer:
<u><em>Group 8 is a group (column) of chemical elements in the periodic table. It consists of iron (Fe), ruthenium (Ru), osmium (Os) and hassium (Hs). They are all transition metals.</em></u>
Explanation:
Answer:
There is one single covalent bond between two carbon atoms.
Explanation:
We know that sharing of electrons form covalent bonds.
If we look upon K,L,M ,N shells of the carbon and hydrogen atoms.
We found that Hydrogen is having only 
electron in K shell.
And Carbon on the other hand is having 
electrons in K shell and 
electrons in L shell.
So carbon have valence electrons,and it can share bonds with any relevant atom to complete its octet.
And Hydrogen requires electron to complete its doublet.
Alkane general formula 
For ethane 
Carbon atom is shared by 
Hydrogen.
The remaining one electron 
of carbon will be shared with another carbon atom.
An image of the sharing of electrons attached below,
Hence we have only covalent bond between the two.
D) An atom with 4 protons, 3 neutrons, and 3 electrons
When you are asked a question like this, you can always ask yourself this question. Can I change it back after this change? For example, if you are burning wood, you cannot bring it back to wood after you burn it, therefore, it is a chemical change. However, if you boil and evaporate water, you can make the water condense again back into its liquid form. In this case, you cannot bring the tomato back to its raw state. Therefore, cooking raw tomatoes is a chemical change.
