A which is element is the answer
When multiple data streams are collected, one must decide how those data will be fused in the decision process. Separate data streams can be:
Mixed mode (including both quantitative and qualitative data).
Redundant (validating the data from another stream).
Complementary (providing measures of multiple characteristics of an object).
Supportive (helping verify some interpretation of another data stream).
Answer: 1.8 micrograms, 1.8 milligrams, 1.8 grams, 1.8 kilograms
Explanation:
Avagadro's law gives the relationship between volume of gas and number of moles of the gas. When the temperature and pressure are constant, volume is directly proportional to number of moles of gas.

V -volume and n - number of moles of gas.
parameters for the first instance are on the left side and parameters for the second instance are on the right side of the equation
initial number of moles n1 - N
n2 - 2N as the number of moles are doubled
V1 - initial volume - 2.10 L
V2 - final volume - V
substituting the values in the equation

V = 4.20 L
final volume is 4.20 L