Correct answer: (c) Only three
Explanation
- A
Only one
Only one. Cobalt, lithium and nickel all appear in common cathode families; the official count is not one.
- B
Only two
Only two. That under-counts the cathode set.
- C
Only three
Only three. Cobalt, lithium and nickel are cathode metals in everyday Li-ion cells. Graphite is the usual anode, so it is the one that drops.
- D
All the four
All four. Graphite is not a cathode material in standard Li-ion cells.
Summary. Official Set A key is (c) only three. In lithium-ion cells the cathode is a lithium metal oxide or phosphate. Cobalt (LCO, NMC), nickel (NMC, NCA) and lithium itself are cathode ingredients. Graphite is the standard anode. LFP has no cobalt or nickel, but the paper still keys three of the four names as the usual cathode set and leaves graphite out. (a)(b) under-count; (d) wrongly keeps graphite.
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