Which molecule contains a total of seven carbon atoms? 2-methyl-heptyne
2-methyl-propane
3-methyl-2-hexene
3-methyl-1-pentene

3-Methylhex-2-ene  

Explanation:

You count the atoms in the stems of the names and add them up.

C. 3-Methylhex-2-ene

           Methyl = 1C

         Hexene = 6C

Methylhexene = 7C

A. 2-Methylhept-1-yne is wrong. It has 1C + 7C = 8C

B. 2-Methylpropane is wrong. It has     1C + 3C = 4C

D. 3-Methylpent-1-ene is wrong. It has 1C + 5C = 6C

a. the law of proportion states the combination of 2 atoms in a specific ratio to produce multiple compounds such as the given statement of question ‘1st compound contains 88.8 % cu ’ indicates 88.8 g of cu is present along with 11.2 g oxygen in 100 g of compound whereas the statement ‘2st compound contains 79.9 % cu ’ indicates 79.9 g of cu is present along with 20.1 g oxygen in 100 g of compound

1st compound contains 88.8 g cu

for cu

m = 63 g /mol

atomic % = 88.8 /63 = 1.42

for o

m = 16 g /mol

atomic % = 11.2 /16 = 0.7

b. the emperical formula of 1st compound is

cu1.4o0.7

cu2o