Arrays with PHP, Jquery & JSON -

i'm looking saving array text file later access, wonder way better save array? opinion question! want know better way save why there null in there on first part?

{     "questionbanknames": "question bank name",     "question": [null, {         "question": "this question 1?",         "type": "manual",         "a": "",         "b": "",         "c": "",         "d": ""     }, {         "question": "this question 2?",         "type": "multi",         "a": "yes",         "b": "no",         "c": "maybe",         "d": "all of above"     }] } 

or

 "questionbanknames": "question bank name",         "question[1][question]": "this question 1?",         "question[1][type]": "manual",         "question[1][a]": "",         "question[1][b]": "",         "question[1][c]": "",         "question[1][d]": "",         "question[2][question]": "this question 2?",         "question[2][type]": "multi",         "question[2][a]": "yes",         "question[2][b]": "no",         "question[2][c]": "maybe",         "question[2][d]": "all of above" 

i prefer storing json format without serializing. makes easier multiple clients consume in future. creating php object json string breeze.

so serialize if not json, save as-is if json.