(a) From the elemental analysis the empirical formula of Compound R is C₂H₄Cl.

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(b) The M⁺ peak at m/z = 126 is evidence that the molar mass is 126 g mol^-1 and hence the molecular formula of Compound R is twice its empirical formula, i.e. C₄H₈Cl₂. 126 g mol^-1 is the molar mass when the isotopes of the two chlorine atoms are both ³⁵Cl. The peak at m/z = 128, the (M+2)⁺ peak, is when one of the Cl atoms is ³⁵Cl and the other ³⁷Cl. The peak at m/z = 140, the (M+4)⁺  peak, is when both of the chlorine atoms are ³⁷Cl.  The fragment at m/z = 63 is due to the molecule being split in half to give C₂H₄³⁵Cl⁺. The smaller peak at at m/z = 65 is due to C₂H₄³⁷Cl⁺. The fragment at m/z = 62 is due to loss of a further proton to give C₂H₃³⁵Cl⁺ with a smaller peak for the analogous fragment containing the other isotope of chlorine, C₂H₃³⁷Cl⁺ at m/z = 64. From its molecular formula and its fragmentation pattern Compound R looks to be a symmetrical dichloroalkane.

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(c) The absorptions at approximately 3000 cm^-1 are due to C–H and the absorption at 650 cm^-1 is likely to be due to the presence of a C−Cl single bond.

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(d) The ¹H NMR spectrum shows that the eight hydrogen atoms are in two different chemical environments in the ratio 3:1. The doublet centred at at 1.6  ppm suggests two separate methyl groups each attached to a carbon atom containing one H atom. Similarly the complex doublet centred at 4.1 ppm suggests two C-H entities each attached to a –CH₃ group and to a –C−H entity

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All this information taken together confirms that Compound R is 2,3-dichlorolbutane, CH₃CHClCHClCH₃.

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