"As I walked around the site, I thought that these days the biggest temple's and mosques and gurudwara is the place where man works for the good of mankind". In these lines Jawaharlal Nehru is talking about:

Bhakra Nangal Dam

The correct answer is Option 3: Bhakra Nangal Dam

A modern and prosperous India, as visualised by Jawaharlal Nehru, was to be built on an edifice of giant steel plants or gigantic dams and power stations. Nehru’s remarks on the Bhakra Nangal dam:

"Our engineers tell us that probably nowhere else in the world is there a dam as high as this. The work bristles with difficulties and complications. As I walked around the site I thought that these days the biggest temple and mosques and gurdwara is the place where man works for the good of mankind. Which place can be greater than this, this Bhakra Nangal, where thousands and lakhs of men have worked, have shed their blood and sweat and laid down their lives as well?"