Which of the following is an alloy?

When finely powdered ore is placed on a rotating grooved table and rotated rapidly,the lighter impurities are removed. What is this method of concentration called?

In the presence of which catalyst is sulphur dioxide heated at high temperature to form sulphur trioxide?

Generally, metals react with acids to produce salt and hydrogen gas. Which of the following acids does not produce hydrogen gas when reacting with most metals (except $Mn$ and $Mg$)?

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 $X, Y, Z$.

On which principle does the method of fractional distillation work?