Which is the best method to determine significant numbers?

The length and breadth of a metal sheet are $3.124\,m$ and $3.002\,m$. The area of the sheet is: (in $,m^2$)

What is the number of significant figures in $3400$?

$A$ body of mass $m = 3.513 \; kg$ is moving along the $x$-axis with a speed of $5.00 \; ms^{-1}$. The magnitude of its momentum is recorded as (Consider significant figures):

Assertion $(A)$: The number $0.00764$ has three significant figures.
Reason $(R)$: If the number is less than $1$,the zeros on the right of the decimal point but to the left of the first non-zero digit are not significant.

For the four sets of three measured physical quantities as given below,which of the following options is correct?
$(i)$ $A_{1}=24.36, B_{1}=0.0724, C_{1}=256.2$
$(ii)$ $A_{2}=24.44, B_{2}=16.082, C_{2}=240.2$
$(iii)$ $A_{3}=25.2, B_{3}=19.2812, C_{3}=236.183$
$(iv)$ $A_{4}=25, B_{4}=236.191, C_{4}=19.5$