What is the number of significant figures in the result of $(3.20 + 4.80) \times 10^5$?

An object of mass $4.237 \, g$ occupies a volume of $1.72 \, cm^3$. The density of the object to appropriate significant figures is ......... $g \, cm^{-3}$.

$A$ person measures the mass of $3$ different particles as $435.42 \ g$,$226.3 \ g$,and $0.125 \ g$. According to the rules for arithmetic operations with significant figures,the sum of the masses of the $3$ particles will be: (in $g$)

For an experimental expression $y=\frac{32.3 \times 1125}{27.4}$,where all the digits are significant. Then to report the value of $y$,we should write $:-$

Statement-$1$: All reliable digits plus the first uncertain digit together are called significant figures.
Statement-$2$: Trailing zero$(s)$ in a number with a decimal point are never significant.

The volume of a sphere is $1.76 \ cm^3$. The volume of $25$ such spheres,taking into account significant figures,is: