Compounds which give the same najor product sn1 and sn2
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Answer:
For starters, none of your products show chirality in any way, so it does not matter whether stereoinformation is lost or whether you convert a racemic mixture into a racemic mixture where every single molecule if you had labelled it pre-reaction now had the opposite stereochemistry — in both cases, both reactants and products are racemic mixtures. So you cannot take the presence or absence of chiraliy to distinguish here.
What we can say, is that every compound can take part in an SN2 reaction (some faster, some slower) but not every one will easily take part in an SN1 reaction. Specificly, (a) and (d) would give a secondary carbocation intermediate while (b) would even give a primary carbocation. These cations are very unstable and would immediately undergo Wagner-Meerwein type rearrangements towards more stable — read tertiary or resonance stabilised — carbocations. Or, to quote one of my professors from uni:
Deciding SN1/SN2/E1/E2, Part 2: The Nucleophile/Base. ... There are likely other products in there. .... is the numerical value for the pKa of a given compound.