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 
Answer:
Having as wide a range of organisms as possible.
Hope it helps! :)
Explanation:
Compounds having same molecular formula but different structural and spatial arrangement are isomers.
Three isomers are possible for dibromomethene.
In one structure (IUPAC name: 1,1-dibromomethene), both the bromine atoms are attached to one carbon atom.
In another two structures (Cis and trans), two bromine atoms are attached to two different carbon atoms.
In Cis 1,2-dibromomethene, two bromine atoms are present on the same side.
Whereas in Cis 1,2-dibromomethene, two bromine atoms are present on the opposite side and hence, does not have net dipole moment.
energy can't be created or destroyed, but mass particles can decay or tranform into others as long as the total mass/energy (remeber E=MC2) is conserved, in nuclear reactions one type of sub-atomic particle change into another, this destabilizes the nucleus forcing it to split and release a certain amount of energy in the form of massless particles