Which is an example of making a quantitative observation?
measuring the mass of metal used in a reaction
recording the color of a solid formed in a reaction
describing a liquid as having a slippery feel
rating an odor on how nice it smells

measuring the mass of metal used in a reaction

Explanation:

In chemistry we analyse any matter in two ways

a) Qualitative: For qualitative analysis we study quality of matter which includes

i) its chemical nature: example organic / inorganic/ cation /anion/ acid/ base / aromatic/ cyclic etc.

ii) its physical nature : example color, odor , viscosity. lubricity, density, temperature, pressure etc.

b) Quantitative: For quantitative analysis we study the quantity of matter.

For example

Mass or volume or mole or concentration etc.

So here measuring the mass of metal used in a reaction is a quantitative observation.

1. 1 mole of anything contains 6.022x10^23 pieces  

d  

2. a  

3. c, number  

5. 1.24x10^24atoms / 6.022x10^23atoms/mole = 2moles h2 atoms  

6. fe2br3 mass = 2moles x mass fe + 3 moles x mass br  

molar mass = grams / number of moles = g/mole  

to find moles = g / molar mass  

to find mass = g = molar mass / moles

- both b and d.

-since b and d are the closest coastlines then that makes it the most affected.

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