Basing himself on the views he elaborated in 1844, were Engels to get into a time machine and come to the US today, what would he argue? America is suffering from too much atheism and not enough religious morality. Because the class divide still exists, America is not a unified country. America is a unified country in which most social layers are committed to their nation and share common set of values and beliefs. Which answer is correct and where did you find the answer?

The best answer to this question is the second one on the list you provide. Engels would probably conclude that the class divide continues to exist in America and that would be the reason he would think that the United States is not a unified country.In 1844, Friedrich Engels published with Karl Marx The Holy Family, followed in 1845 by The Condition of the Working Class. The earlier work is a prelude to their fuller indictment of class divisions.There is considerable discussion available of the widening class gap in the U.S. today. A recent study with substantial data is available from the Pew Research Center. You might find it helpful. It argued that the wealth gap between upper class and middle class American families has grown to record levels, is more pronounced along racial and ethnic lines, and has increased even more since the Great Recession of 2007-2009.
https://www.pewresearch.org/fact-tank/2014/12/17/wealth-gap-upper-middle-income/