Choose the exact meaning of the idiom/ phrase. He is not worth his salt if he fails at this juncture.

Quite worthless is the exact meaning of the idiom/ phrase.
'very strange' can be expressed as an abnormal situation. For instance, It was very strange of her to skip the office party.
'very proud of himself'. This is basically used in a situation when a person praises himself or herself for some of his/her action. For instance, He was very proud of himself after donating a large amount to the cancer fund.
'quite depressed'. This set of words can be used in a sentence such as, Radha was quite depressed for not being able to participate in the competition.
'quite worthless'. This phrase can be used in a sentence such as, He will become quite worthless as the disease plants do to the farmer.
As per the meaning of the idiom as we have described above, we can see that the fourth option is appropriate to signify the meaning of given idiom. Thus, the words or phrase quite worthless would be the correct choice here.