Answer:
56°
Explanation:
First calculate 

The interplanar spacing can be calculated from:

The diffraction angle is determined from:

Solve for 

The diffraction angle is:

Answer:
A. Water
Explanation:
H2O means that there are two hydrogen and one oxygen in every water molecule.
Answer:
54
Barium atomic number is 56, this means that it has 56 protons in its nucleus and put it as a period 6 element. an uncharged barium atom would have 56 electron also. However as a group 2 element barium easily loses 2 electron to form the +2 cation. the ions has 56-2=54
Gaining of electrons is reduction and loss of electrons is oxidation.
<em>Hope this helped! :)</em>