Kepler stated three laws of planetary motion.
First law states that the pathway of a planet is an ellipse with the Sun at one of the foci.
Second law states that an imaginary line joining the Sun and a planet sweeps out equal areas during equal lengths of time.
Third law states that the square of the period of the orbit of a planet is directly proportional to the cube of the length of the distance from the Sun.
Therefore, the answer is that Kepler's second law of planetary motion states that planets cover the same area during equal time periods.
Answer : The amount of formaldehyde permissible are, 
Explanation : Given,
Density of air =

First we have to calculate the mass of air.



Now we have to calculate the amount of formaldehyde.
Permissible exposure level of formaldehyde = 0.75 ppm = 
Amount of formaldehyde in 7.2 g of formaldehyde = 
Amount of formaldehyde in 7.2 g of formaldehyde = 
Thus, the amount of formaldehyde permissible are, 
Answer:
Explanation:
Its simple
This is the number of atoms, ions, or molecules that a central atom or ion holds as its nearest neighbours in a complex or coordination compound or in a crystal.
for example: Sodium chloride (NaCl) or table salt is an ionic compound. It means that each cation will have exactly one anion associated with it, which means the cation Na+ and the anion Cl− have the same number of coordinates.
It may be really confusing at first
I recommend you go online and watch tutorial videos on the topic
3.9 grams CaCO3
The mass of 2.0 L of water with a density of 1.00 g/ml is 2000 grams.And 1 ppm of that is 2000 / 1000000 = 0.002 grams. So just multiply by the ppm of CaCO3, giving 0.002 g * 1.95x10^3 = 3.90 grams.
Since the least accurate datum we have is 2 significant figures, the result should be rounded to 2 significant figures, giving 3.9 grams.