Which of the following is considered a contact force? Group of answer choices

friction between an object and chair

the force between two magnets

the force between two charged particles

the gravitational pull of a planet

☑ Friction between an object and chair

☐ The force between two magnets

☐ The force between two charged particles

☐ The gravitational pull of a planet

number of molecules / avogadro's number * molecule molecular = mass

explanation:

we define a gram-molecular weight as the mass of one mole of any element or compound. a mole contains avogadro's number of units (molecules) –  

6.022

x

10

23

. so, dividing the number of molecules by avogadro's number gives us the number of moles. multiplying that by the molecular weight gives us the mass. from the periodic table we find the gram-molecular weight of u to be238 and of f to be19. so,  

u

f

6

will have a gram-molecular weight of 352g.

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