What volume of solution must be added to 4.0 mol of NaCl to make a 1.2 M solution?

Explanation:

Molarity is a measure of concentration in moles per liter.

The solution has a molarity of 1.2 M or 1.2 moles per liter. There are 4.0 moles of NaCl, the solute. We don't know the liters of solution, so we can use x.

Substitute the values into the formula.

Since we are solving for x, we must isolate the variable. Begin by cross multiply (multiply the 1st numerator and 2nd denominator, then the 1st denominator and 2nd numerator.

x is being multiplied by 1.2 moles per liter. The inverse of multiplication is division, so divide both sides by 1.2 mol/L

The units of moles (mol) will cancel.

The original measurements both have 2 significant figures, so our answer must have the same. For the number we found, this is the tenths place.

The 3 in the hundredth place tells us to leave the 3 in the tenths place.

Approximately  3.3 liters of solution are needed to make a 1.2 M solution with 4.0 moles of sodium chloride.

A. scientists have discovered new planets orbiting a star by detecting a wobble in the star's motions.

Explanation:

As can be seen from the options only first option shows an observation. Here the scientists observed the wobbling of the stars and through that they deduced that there will be planets orbiting around that star. This deductions stands true as the gravity of the planet affects the motion of the star as well. Other options do not show such instances.