The ratio of acetylene to oxygen is approximately ................ for neutral flame used in gas welding

In $$DC$$ welding, the straight polarity (electrode negative) results in

In an explosive welding process, the ..................... (maximum/minimum) velocity of impact is fixed by the velocity of sound in the ............. (flyer / target) plate material.

For resistance spot welding of $$1.5$$ $$mm$$ thick steel sheets, the current required is of the order