How many moles are present in 1.25x1023 molecules of salt (NaCl)?

0.21 mole of NaCl

Explanation:

From the question,

using Avogadro's Constant,

1 mole of every compound contains 6.02×10²³ molecules of that compound.

I.e

1 mole of NaCl ⇒ 6.02×10²³ molecules of NaCl

x moles of NaCl ⇒ 1.25××10²³ molecules of NaCl

Solving for x,

x moles of NaCl = (1 mole of NaCl)×(1.25×10²³ molecules of NaCl)/(6.02×10²³ molecules of NaCl)

x moles of NaCl = (1×1.25×10²³)/6.02×10²³

x = 0.208 mole of NaCl

x ≈ 0.21 mole of NaCl

it's c. elements are placed in rows based on how may valencies electrons have.

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.