Questions

During convection, cool and dense air falls through the warmer and less dense air. The warm air having less mass is being displaced by the cooler which is much heavy. Convection always involves the air rising through the atmosphere.

Ecology is the branch of science which deals with the study of Ecosystem (relation between the Organisms and their Environment.)

The first bank established in India in the year 1770 was Bank of Hindustan followed by the General Bank of India in the year 1786. The State Bank of India (SBI) was the still existing oldest bank which was established in the year 1806 in the name of Bank of Calcutta.

Microsoft Excel is a spreadsheet developed by Microsoft for Windows, macOS, Android and iOS. It features calculation, graphing tools, pivot tables, and a macro programming language called Visual Basic for Applications.

Normal Gas welding use oxygen-acetylene.

Depending on what materials you are welding, there are some more options that might be used.

For example - MIG/TIG use Argon, MAG use an argon-something mix.

An up - selling is getting the customer to spend more money, buy a more expensive model of the same type of product, or add features or warranties that relate to the product viewed or purchased. 

A cross - sell is to get the customer to spend more money by adding more products from other categories than the product being viewed or purchased. 

Optical illusion is what that refers to persistence of vision with a principle that multiple images blend into a single image in human mind and what is showed in cinema.

Hence, Persistence of vision is the principle behind cinema.