= Solution
Apply part i to the short exact sequence of trivial $G$-modules
$$
0\longrightarrow\mathbb Z\longrightarrow\mathbb Q
\longrightarrow\mathbb Q/\mathbb Z\longrightarrow0.
$$
The relevant segment is
$$
H^1(G,\mathbb Q)\longrightarrow H^1(G,\mathbb Q/\mathbb Z)
\xrightarrow{\delta}H^2(G,\mathbb Z)
\longrightarrow H^2(G,\mathbb Q).
$$
Both outer groups vanish by parts a(iv) and a(v), so the <connecting homomorphism> is an isomorphism:
$$
\boxed{H^2(G,\mathbb Z)\cong H^1(G,\mathbb Q/\mathbb Z)}.
$$
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