The spontaneity means, having the potential to proceed without the assistance of external agency. The processes which occur spontaneously are

1.  flow of heat from colder to warmer body

2. gas in a container contracting into one corner

3. gas expanding to fill the available volume

4.  buring carbon in oxygen to give carbon dioxide

(c, d)
Options (a) and (b) can neither occur by themselves nor by initiation, (c) can occur by itself, (d) occur on initiation. Flowing of heat from warmer to colder body, expanding of gas and buring of carbon to give carbon dioxide, all are spontaneous process.