In this question, you're asked to identify what Dr. Samuel Johnson's opinion was regarding Shakespeare's plays and the classical unities. Johnson wrote about this in the preface to his edition of Shakespeare's works, and his views can be summarized as follows:
Unity of Action (which concerns the focus on a single plot or theme): Johnson praised Shakespeare for satisfying this unity in most of his plays. Shakespeare often maintained the unity of action by centering on a primary plot or conflict, even if there were subplots. So, Statement II ("Shakespeare followed the important Unity of Action satisfactorily") is correct.
Unity of Time and Unity of Place (which require that the action occurs within a single day and location, respectively): Johnson argued that these unities are based on "false assumptions." He believed that audiences are willing to suspend their disbelief when watching plays, and therefore, strict adherence to these unities isn't necessary. Shakespeare, according to Johnson, did not harm his plays by disregarding these unities. So, Statement IV ("Unity of Time and Place arise from false assumptions") is also correct.
Now, let's look at why the other statements are incorrect:
Statement I ("Shakespeare should have followed the Unities"): This is incorrect because Johnson did not think Shakespeare was wrong in ignoring the unities of time and place. In fact, he argued the opposite, that they are based on false assumptions.
Statement III ("Shakespeare’s plays suffered because they did not follow the Unities"): Johnson did not believe that Shakespeare's plays were weakened by ignoring the unities of time and place. He defended Shakespeare's disregard for these conventions.
Thus, the correct answer is 2 (II and IV are correct).