Answer:- Mole ratio of D to A is 4:3.
Explanations:- Mole ratio for a chemical reaction is the ratio of the coefficients.
The given generic chemical reaction is:

The numbers written in front of each chemical species in the chemical reaction are their moles. For the given generic chemical reaction the coefficient of A is 3 and that of B is 1. So, the mole ratio of A to B is 3:1.
Similarly if we want to write the mole ratio of C to D then it is 1:4.
We are asked to write the mole ratio of D to A. So, like the other ratios, the mole ratio of D to A is 4:3 as the coefficient of D is 4 and A is 3.
Answer:
the mass of 2.9 moles of calcium is 116 g
Explanation:
The computation of the mass of 2.9 moles of calcium is shown below
As we know that
Mole = mass ÷ molar mass
where,
Moles be 2.9
And, we know that the molar mass of calcium be 40g/mol
Now put the values to the above formula
2.9 = Mass ÷ 40
So, the mass would be
= 40 × 2.9
= 116 g
Hence, the mass of 2.9 moles of calcium is 116 g
Answer:
To allow all the elements or compounds to separate complete.
Explanation:
In chromatography, the compounds need some space and time to separate, one from each other, if you just use the half of the paper strip maybe you will not notice the different spots of compounds. Remember all the substances have different affinity for the solvents, that means, some react very quickly but others need more time as the colors that conform the black color in an ink.