How many L of 3.0M solution
can be made with 78g of
NaCl?

Need to find moles NaCl.

526 grams NaCl (1 mole NaCl/58.44 grams)

= 9.0 moles NaCl

now,

Molarity = moles of solute/Liters of solution

or, for our purposes

Liters of solution = moles of solute/Molarity

Liters of solution = 9.0 moles NaCl/3.0 M

= 3.0 liters in volume

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.