All of the following would be questions that could be scientifically investigated except:

a. what is the proper number of children to have in today's family?
b. will equal sizes of styrofoam and wood have the same mass?
c. does adding salt to water raise its boiling point?
d. does lack of sunlight affect plant growth?

option A: What is the proper number of children to have in today's family?

A scientific investigation includes a scientific method to approach a problem. There is a systematic approach is used to address a problem. It generally includes five steps: first a problem needs to be identified. Thereafter, a background research is important to form a hypothesis. Fourthly, an experiment, observation or measurements are done in order to draw conclusions at last.

From the given questions, option A is a question which cannot be scientifically investigated. This is because, it varies from individual to society to the economy of a state.  The conclusion would not be generalized solution.

option B.Will equal sizes of Styrofoam and wood have the same mass?  can be scientifically investigated. The given quantities can be measured and tested.

C. Does adding salt to water raise its boiling point?  This can be scientifically tested

D. Does lack of sunlight affect plant growth? This can also be scientifically measured.

mass and volume are the answers you are looking for