The low-resolution NMR spectrum of a compound provides information about the number of chemically distinct hydrogen atoms in the molecule. In order to determine the number of peaks expected in the NMR spectrum of vinyl chloride and ethyl cyclopropane, we need to analyze the chemical structure of these compounds and identify the different sets of hydrogen atoms.

1. Vinyl Chloride:
- Vinyl chloride has the molecular formula C2H3Cl, which means it contains two carbon atoms, three hydrogen atoms, and one chlorine atom.
- The carbon atoms in vinyl chloride are chemically distinct from each other, as one is bonded to the chlorine atom and the other is attached to the vinyl (C=C) group.
- The hydrogen atoms in vinyl chloride can be classified into two sets: those attached to the carbon atom bonded to chlorine (C-H) and those attached to the carbon atom in the vinyl group (C=C-H).
- Therefore, vinyl chloride is expected to exhibit three peaks in the low-resolution NMR spectrum: one for the C-H protons and two for the C=C-H protons.

2. Ethyl Cyclopropane:
- Ethyl cyclopropane has the molecular formula C5H10, which means it contains five carbon atoms and ten hydrogen atoms.
- The carbon atoms in ethyl cyclopropane can be divided into three sets: the two carbons in the cyclopropane ring (ring carbons), the carbon in the ethyl group (ethyl carbon), and the carbon in the methyl group (methyl carbon).
- The hydrogen atoms in ethyl cyclopropane can also be divided into three sets: those attached to the ring carbons (C-H), those attached to the ethyl carbon (C-C-H), and those attached to the methyl carbon (C-H3).
- Therefore, ethyl cyclopropane is expected to exhibit five peaks in the low-resolution NMR spectrum: two for the C-H protons, two for the C-C-H protons, and one for the C-H3 protons.

Based on the analysis of the chemical structures, the correct answer is option 'A' - 3 peaks for vinyl chloride and 5 peaks for ethyl cyclopropane.