Which of the following is a latex-based alkaloid?

An organic compound with the molecular formula $C_3H_6O$ does not give a precipitate with $2,4-$dinitrophenylhydrazine and does not react with sodium metal. What is this compound?

Changes in $GnRH$ pulse frequency in females is controlled by circulating levels of

The following series $L-C-R$ circuit,when driven by an emf source of angular frequency $70 \text{ krad/s}$,the circuit effectively behaves like:

$A$ transformer works on the principle of

The $\pi$-acid ligand which uses its $d$-orbital during synergic bonding in its complex compound is