The correct crontab entry to execute the script chklog once per hour between 3 p.m. and 5 p.m. on Monday and Thursday each week is:

Uses 3,4,5 for hours which represents 3 AM to 5 AM, not 3 PM to 5 PM, and uses day values 2,5 which correspond to Tuesday and Friday, not Monday and Thursday.

Uses 3,4,5 for hours which represents 3 AM to 5 AM rather than 3 PM to 5 PM in 24-hour notation, even though the day-of-week values 1,4 are correct.

The crontab format is: minute hour day-of-month month day-of-week. Running once per hour at the top of the hour requires minute=0. 3 PM, 4 PM, and 5 PM in 24-hour format are 15, 16, and 17. Monday=1 and Thursday=4 in crontab day-of-week numbering (0=Sunday), so '0 15,16,17 * * 1,4 chklog' is the correct and complete entry.

Places the day values 1,4 in the day-of-month field (third field) instead of the day-of-week field (fifth field), so it would run on the 1st and 4th of every month rather than on Monday and Thursday.

Uses '*' for the minute field instead of '0', which would execute the script every minute during those hours rather than once per hour.