Which from following compounds is least soluble in water at STP?

Which of the following statements is correct about $\mathrm{O}_2$ and $\mathrm{O}_3$ molecule?

What is the total number of donor atoms present in Tetracyanonickelate(II) ion?

Half life of a first order reaction is 900 minute at 400 K , find its half life at 300 K ?

$$ \left(\frac{\mathrm{E}_{\mathrm{a}}}{2.303 \mathrm{R}}=1.3056 \times 10^3\right) $$