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Option B is correct

Option D is incorrect as it means **Every graph is not connected** which is different from **Not every graph is connected****Not every graph is connected**

It can be rewritten as:

**There is a graph which is not connected**

so ∃x(graph(x) ⋀ ¬connected(x)

or another way to do it ,simply:

¬∀x(graph(x) → connected(x))

∃x¬(graph(x) → connected(x)) (negation rule)

∃x¬(¬(graph(x) ⋁ connected(x))

And finally

∃x(graph(x) ⋀ ¬connected(x))