Vygotsky's concept of zone of proximal development refers to:. a) children's ability to estimate how much they know.
b) the range of tasks children can perform by themselves.
c) the degree of maturation necessary to accomplish complex physical tasks.
d) the range of tasks children can accomplish only with support.

d) the range of tasks children can accomplish only with support.

Explanation:

The zone of proximal development may be defined as the as the zone of the  most immediate  mental or psychological development of the learners which includes a vast range of their  cognitive, volitional, psychological and emotional processes.

In other words it is the difference between what a person or a learner can perform without help and what they can achieve or do with the guidance and the encouragement of a skilled partner.

Thus the task that the children can master or do with the help from a trained person or with support refers to the concept of proximal development.

This concept was given by Lev Vygotsky.

if im not mistaken its a. collective emotional arousal