Which of the following backup technique is most space efficient? a. Full backup b. Incremental backup c. Differential backup

First of all take Full Back up 

incremental is the most space efficient, but a full backup should be taken 1st

b. incremental backup

Everyday go for incremental backup.

Incremental backups are the most space efficient backup, First of all take Full Backup , Everyday go for incremental backup.

At first you take full backup then every day go with the incremental backup because incremental backup only backs up the changes from the last incremental backup.

c. Differential backup is most space efficient

incremental backup, but incremental backups is the slowest because it may require several sets of data to fully restore all the data

Incremental backups are the most space efficient backup technique.

First of all take Full Back up , Everyday go for incremental backup.