Which of the following has the least mass?

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

Select the correct option based on the given figure. Symbol $T$ indicates a true statement and $F$ indicates a false statement.
Solution $P = 8 \, N$ $H_2SO_{4(aq)}$ and Solution $Q = 8 \, N$ $HNO_{3(aq)}$.
$(1)$ The number of moles of solute in solution $P$ and solution $Q$ are equal.
$(2)$ The number of gram-equivalents of solute in solution $P$ and solution $Q$ are equal.
$(3)$ The mole fraction of solvent in solution $P$ and solution $Q$ are equal.
$(4)$ The concentration of $H^+_{(aq)}$ in solution $P$ and solution $Q$ are equal.

Bleaching powder and bleach solution are produced on a large scale and used in several household products.
The effectiveness of bleach solution is often measured by iodometry.
$1.$ $25 \ mL$ of household bleach solution was mixed with $30 \ mL$ of $0.50 \ M \ KI$ and $10 \ mL$ of $4 \ N$ acetic acid. In the titration of the liberated iodine,$48 \ mL$ of $0.25 \ N \ Na_2S_2O_3$ was used to reach the end point. The molarity of the household bleach solution is
$(A)$ $0.48 \ M$ $(B)$ $0.96 \ M$ $(C)$ $0.24 \ M$ $(D)$ $0.024 \ M$
$2.$ Bleaching powder contains a salt of an oxoacid as one of its components. The anhydride of that oxoacid is
$(A)$ $Cl_2O$ $(B)$ $Cl_2O_7$ $(C)$ $ClO_2$ $(D)$ $Cl_2O_6$
Give the answer for question $1$ and $2.$

Write formulas for the following compounds:
$(1)$ Mercury $(II)$ chloride
$(2)$ Nickel $(II)$ sulphate
$(3)$ Tin $(IV)$ oxide
$(4)$ Thallium $(I)$ sulphate

When $400 \ mL$ of $0.2 \ M \ H_2SO_4$ is mixed with $600 \ mL$ of $0.1 \ M \ NaOH$, the heat evolved is $3.43 \ kJ$. If the specific heat of water is $4.18 \ J \ K^{-1} \ g^{-1}$, the rise in temperature of the final solution will be ........... $K$. (Assume the specific heat capacity of the final solution is the same as that of water)