Answer:
I guess covalent bond is formed
C. a change of state. It can be a physical or a chemical state of change.
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:
The answer to your question is: letter D.
Explanation:
Double replacement reaction is when the cation of one reactant replaces the metal of the other reactant and vice versa.
a. 2SO2 + O2 —> 2S03 This is a combination reaction
b. Zn + Cu(NO3)2 → Zn(NO3)2 + Cu This is a single replacement reaction.
c. 2H2O2–> 2H2O + O2 This is a decomposition reaction
d . AgNO3 + NaCl → AgCl + NaNO3 This is a double replacement reaction
