For a transition metal M, the correct order of

spectral shift [in ppm relative

Correct option is A

¹²C being non-magnetic (spin number, I = 0) is NMR inactive. Like ¹H nucleus, ¹³C has spin number, I=1/2, therefore principles governing ¹³C NMR are exactly similar to those of ¹H NMR spectroscopy, but the scale of observed shifts and couplings is greater for ¹³C. Chemical shifts for ¹³C are measured (in ppm) from tetramethyl silane (TMS) as reference so that the same sample can be used to study both nuclei. The δ scale for TMS is 0.0, for ¹H is 0-15 ppm and for ¹³C is 0-250 ppm. Because of the greater range of chemical shifts ¹³C spectra nearly always contain a separate and distinct resonance for each chemically shifted nucleus in the molecule.
Coupling between ¹³C and neighbouring protons exhibits in ¹³C NMR spectra. As in ¹H NMR spectra, the pattern of coupling is also very diagnostic. A C-H fragment gives a doublet, CH₂ gives a triplet and CH₃ gives a quartet in the ¹³C NMR spectrum. This reveals the number of protons to which each carbon atom is bound.
The magnetic moment of ¹³C is about one quarter that of ¹H, therefore, the signals in ¹³C NMR spectrum are weaker. ¹³C is 1.6% sensitive as ¹H.
¹³C-¹³C coupling is negligible because natural abundance of ¹³C is only 1.1 per cent. Thus, in one type of ¹³C NMR spectrum (proton decoupled) each magnetically non-equivalent carbon gives a single sharp peak that does not undergo further splitting. If there are fewer than 100 carbon atoms in a molecule, then there will be, on an average, only one ¹³C nucleus in the molecule.
It is usually possible to get good proton decoupled ¹³C NMR spectra from most of the organometallic compounds. Approximate ranges of chemical shifts for ¹³C NMR spectra of certain groups in organometallic compounds are shown in Table.