Which of the following is a geometric series?

The geometric series is:

               2+14+98+686

The geometric series is a series in which each term of the series is a constant multiple of the preceding term of the series.

a)

6+13+20+27

This is not a geometric series but is a arithmetic series.

Since, each term is increased from the preceding term by 7.

Since, 6+7=13

13+7=20

20+7=27

b)

7+21+35+45

This is not a geometric  series.

Since 7×3=21

But 21×3=63

But the next term that is given is: 28 and not 63

c)

14+21+28+35

This is a arithmetic sequence.

Since

14+7=21

21+7=28

and 28+7=35

d)

2+14+98+686

This is a geometric sequence.

Since,. we get a common ratio i.e. a term which when multiplied to each term of sequence gives the next term of the series.

i.e. 2×7=14

14×7=98

98×7=686