All of the digits in 23139 are significant. If you are not specifying a certain number of sig figs, then the answer is 23139.
23100
23100
0.000709999 rounded to 3 significant figures is 0.000710
That depends on how many significant figures you are talking about.If three significant figures then 700 is the largest that rounds to 700.If four significant figures are to be rounded to three significant figures then 700.4If five significant figures are to be rounded to three significant figures then 700.49If six significant figures are to be rounded to three significant figures then 700.499etc.
0.00076321cg rounded to three significant figures is 0.000763cg
23100
23100
It is 6.7 when rounded to 2 significant figures
You didn't say how many significant figures. But, rounded to six significant figures it would be 5206.00
0.00721004 rounded into three significant figures is 0.00721
16.275 rounded to 3 significant figures is 16.3
79,966.92 rounded to three significant figures is 8.00e4
0.00721004 rounded to three significant figures is 0.00721
44.981 rounded to three significant figures is 45.0
0.000709999 rounded to 3 significant figures is 0.000710
223.4016 rounded five significant figures is 223.40
9,682 rounded to three significant figures is 9,680.