What is the typical carat value of gold used in jewelry?

When a metal $X$ is treated with cold water,it gives a basic salt $Y$ with molecular formula $XOH$ (Molecular mass $= 40$) and liberates a gas $Z$ which easily catches fire. Identify $X, Y, Z$.

Why is sodium chloride soluble in water but not soluble in kerosene?

When an aqueous solution of ammonia is added to an aqueous solution of cupric sulfate,which substance forms a pale blue precipitate?

What is the percentage of $H_{2}SO_{4}$ in dilute sulfuric acid (in $\%$)?

What is the chemical formula for potassium dichromate?