A forensic analyst examines a sample of black ink recovered from a crime scene suspect using thin-layer chromatography (TLC). The suspect's ink is compared to four reference ink brands: A, B, C, and D, as shown in the chromatogram below.
a.[2]
Calculate the RfR_{\text{f}}Rf value for brand B. Give your answer to 2 significant figures.
b.[1]
Which of the reference ink brands are shown to be present in the suspect's ink?
c.[1]
Suggest why brand D has not travelled as far up the plate as brand B.
d.[2]
State one similarity and one difference between gas chromatography and thin-layer chromatography.
e.[1]
Explain why thin-layer chromatography is used instead of gas chromatography to analyse the ink.