$\mathrm{Na}, \mathrm{Mg}, \mathrm{Al}$ and $\mathrm{S}$ belong to $3^{\mathrm{rd}}$ period of the periodic table. Out of these, the acidic oxide is formed by

An element X (atomic number 20) reacts with another element Y (atomic number 17) to form a compound X. Which of the following statement are true regarding compound Z. Which of the following statement are true regarding this compound?

I. Molecular formula of of X is ${\mathrm{XY}}_2$.

II. X and Y are joined by sharing of electrons.

III. Z imparts characteristic flame colour.

IV. It is soluble in water.

An element $\mathrm{X}$ forms two oxides $\mathrm{XO}$ and ${\mathrm{XO}}_2$. The oxide $\mathrm{XO}$ is neutral but ${\mathrm{XO}}_2$ is acidic in nature.The element $\mathrm{X}$ is most likely to be 

Four elements W, X, Y, and Z have atomic numbers 12,18, 4, and 16:

Which of the above will form an acidic oxide?

An equal volume of molar hydrochloric acid and sulphuric acid is neutralised by dilute $\mathrm{NaOH}$ solution and $\mathrm{x} \mathrm{Kcal}$  and $\mathrm{y} \mathrm{Kcal}$ of heat are liberated. Which of the following is true? 

Which of the following pair of compounds cannot exist together in a solution?