Answer:- 3. 
and 
Explanations:- An empirical formula is the simplest whole number ratio of atoms of each element present in the molecule/compound.
For example, the molecular formula of benzene is 
. The ratio of C to H in it is 6:6 that could be simplified to 1:1. So, an empirical formula of benzene is CH.
In the first pair, the ratio of C to H in first molecule is 2:4 that could be simplified to 1:2 and the empirical formula is 
. In second molecule the ratio of C to H is 6:6 and it could be simplified to 1:1. and the empirical formula is CH. Empirical formulas are different for both the molecules of first pair and so it is not the right choice.
In second pair, C to H ratio in first molecule is 1:2, so the empirical formula is . The C to H ratio for second molecule is 1:4, so the empirical formula is 
. Here also, the empirical formulas are not same and hence it is also not the right choice.
In third pair, C to H ratio in first molecule is 1:3, so the empirical formula is . In second molecule the C to H ratio is 2:6 and it is simplified to 1:3. So, the empirical formula for this one is also . Hence. this is the correct choice.
In fourth pair, first molecule empirical formula is CH. Second molecule has 2:4 that is 1:2 mole ratio of C to H and so its empirical formula is . As the empirical formulas are different, it is not the right choice.
So, the only and only correct pair is the third one. 3. and
The answer for the following question is explained below.
Therefore the total number of orbitals are " 9 ".
Explanation:
Orbital:
An orbital is a mathematical function that describes the wave-like behavior of an electron,electron pair,or the nucleons.
The total number of orbitals present in the 3rd energy level is 9.
Here,
A 3 s subshell has only one orbital.
A 3 p subshell has three orbitals.
A 3 d subshell has five orbitals.
Therefore the total number of orbitals is:
3 s = 1 orbital
3 p = 3 orbitals
3 d = 5 orbitals
total orbitals in 3rd energy level is = 1 + 3 + 5 =9
Therefore the total number of orbitals are " 9 ".
<span>A sample that weighs 107.75 g is a mixture of 30% helium atoms and 70% krypton atoms. How many particles are present in the sample? </span>3.59
