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Two: 1,1-dichloroethane and 1,2-dichloroethane.
CH3CH-Cl2
I guess it is 1,2-Dichloroethane
The molecule is symmetric so all protons are equivilent. Equivilent protons cannot couple with each other, so the spectrum is a singlet.
YES! dichloromethane, dichloroethane, chloroform are the examples