1 Na = 23 g/mol
1 mole of Na atom contain an Avogadro Number of atoms .
23g of Na Na atom contain 6.02 * 10²³ atoms.
175 g of Na will contain: 175 * <span>6.02 * 10²³ / 23
</span>
≈ 4.580 * 10²⁴ atoms of Na.
<span>Mass percentage is one way of representing the concentration of an element in a compound or a component in a mixture. </span>To calculate percent by mass, you need to determine two things: the mass of just the element, and the molar mass of the whole compound. We calculate as follows:
.10 g NaCl / g NaCl + Water = ( 10.0 g NaCl + x ) / (10.0 g + 255 g + x )
x = 18.33 g NaCl needed
The cloud with those characteristics is #1