It's not entirely clear to me, what you are trying to accomplish. It is much easier to get help, if you supply a reproducible example also please look into code formatting using backticks.
Perhaps you're looking for something like this:
library("tidyverse")
set.seed(182635)
d = tibble(Open = rnorm(n = 250, mean = 100),
High = rnorm(n = 250, mean = 100),
Low = rnorm(n = 250, mean = 100),
Close = rnorm(n = 250, mean = 100))
d = d %>% mutate(Serial = 1:nrow(.))
d
# A tibble: 250 x 5
Open High Low Close Serial
<dbl> <dbl> <dbl> <dbl> <int>
1 101. 99.3 100. 100. 1
2 101. 102. 98.4 98.2 2
3 101. 100. 100. 101. 3
4 101. 102. 103. 99.9 4
5 98.2 102. 101. 98.6 5
6 101. 100. 98.2 102. 6
7 98.4 100. 99.4 101. 7
8 102. 98.5 101. 99.2 8
9 99.4 99.7 101. 101. 9
10 101. 99.8 100.0 101. 10
# ... with 240 more rows
d %>% summarise(Max_Vals = max(Close), Serial = which.max(Close))
# A tibble: 1 x 2
Max_Vals Serial
<dbl> <int>
1 103. 149
More information on how to get help, can be found here 