Which of the following is an example of how a scientist might use a model

a. marbles placed inside a hollow sphere are used to describe protons in a nucleus

b. stopwatches measure the amount of time it takes for runners to complete a mile

c. microscopes are used to magnify a group of cells on sets of slides

d. a wrench is used to tighten a nut onto a piece of wood

A. Marbles placed inside a hollow sphere are used to describe protons in a nucleus.

it would be A because the other options are just the tools used in an experiment and A is actually using other objects

given:

mass of na = 115 g

excess cl2

to determine:

mass of nacl produced

explanation:

given reaction is-

2na(s) + cl2(g) → 2nacl(s)

since cl2 is in excess, na will be the limiting reagent

as per the reaction stoichiometry na: nacl = 1: 1

i.e. moles of na reacted = moles of nacl formed

now, # moles of na = mass of na/atomic mass

                                  = 115 g/23 g.mol-1 = 5 moles

therefore, moles of nacl = 5

molar mass of nacl = 58 g/mol

mass of nacl = 5 moles * 58 g.mol-1 = 290 g

ans: amount of nacl produced = 290 g