Answer:
The molar concentration of Cu²⁺ in the initial solution is 6.964x10⁻⁴ M.
Explanation:
The first step to solving this problem is calculating the number of moles of Cu(NO₃)₂ added to the solution:

n = 1.375x10⁻⁵ mol
The second step is relating the number of moles to the signal. We know the the n calculated before is equivalent to a signal increase of 19.9 units (45.1-25.2):
1.375x10⁻⁵ mol _________ 19.9 units
x _________ 25.2 units
x = 1.741x10⁻⁵mol
Finally, we can calculate the Cu²⁺ concentration :
C = 1.741x10⁻⁵mol / 0.025 L
C = 6.964x10⁻⁴ M
The answer should be B, ionic bond.
Ionic bond is the bonding between a metal and a non-metal. While covalent bond is the bond between non-metals, and metallic bond is the bond between metals.
Since Na, sodium, is a metal, and Cl, chlorine, is a non-metal, the bond formed between them is an ionic bond. Sodium gives up an electron to chlorine inside this bonding.
<span>The element that is used in light bulbs as a filament is tungsten - this is almost always the case in halogen and incandescent bulbs. Tungsten is chosen for this purpose because of the fact it can withstand temperatures of up to 4,500 degrees, as well as being incredibly flexible.</span>