Which of the following has the minimum number of oxygen atoms?

What quantity (in $mL$) of a $45\%$ acid solution of a mono-protic strong acid must be mixed with a $20\%$ solution of the same acid to produce $800 \ mL$ of a $29.875\%$ acid solution?

What is the percentage of lead in a lead pencil (in $\%$)?

Iron sulphide is heated in air to form $A$,an oxide of sulphur. $A$ is dissolved in water to give an acid. The basicity of this acid is

You are given $500 \ mL$ of $2 \ N \ HCl$ and $500 \ mL$ of $5 \ N \ HCl$. What will be the maximum volume of $3 \ M \ HCl$ that you can make from these two solutions? .............. $mL$

$1 \, L$ aqueous solution of $H_{2}SO_{4}$ contains $0.02 \, mmol$ of $H_{2}SO_{4}$. $50 \%$ of this solution is taken and diluted with deionized water to give $1 \, L$ solution $(A)$. In solution $(A)$, $0.01 \, mmol$ of $H_{2}SO_{4}$ is added. The total amount of $H_{2}SO_{4}$ in the final solution is $x \times 10^{-3} \, mmol$. The value of $x$ is: