Q: 32 (NDA-II/2011)

All the elements in a group (family) have a common valency. For example, all the elements of the carbon family (carbon, silicon, germanium, tin and lead) have common valency four. However, some of these elements can also have valency two.
Which of the following can have valency two?
question_subject: 
Science
question_year: 
2011
question_exam: 
NDA-II
stats: 
0,32,192,72,72,40,40