Questions

The missing number in the given number puzzle is "78".

Here the logic is the numbers are from 86 - 91 when we read upside down.

In music, a fugue is a contrapuntal compositional technique in two or more voices, built on a subject that is introduced at the beginning in imitation and which recurs frequently in the course of the composition. 

Hence, the main theme of a fugue is called the subject.

Paper production is basically a two-step process in which a fibrous raw material is first converted into pulp, and then the pulp is converted into paper. The harvestedwood is first processed so that the fibres are separated from the unusable fraction of the wood, the lignin. Pulp making can be done mechanically or chemically. In the chemical pulping process, alkali (e.g., sodium hydroxide in the form of a lye or caustic soda) is usually used to remove the lignin that binds the fibres. So, for degumming of raw material, caustic soda is used.

Amazon, is an American electronic commerce and cloud computing company.

Payment gateways process credit card payments and other forms of internet transactions, in a secured format via any website or web-enabled device. They facilitate these transactions by transferring critical information between payment portals and the front-end processor, which is usually a bank.

Amazon uses its own payment gateway Amazon Pay Payment gateway.

Energy tranfer takes place either by means of Heat or Work only in Thermodynamics.

Heat :: Heat Energy is defined as Energy that can be transferred due to temperature change.

Whereas

Thermal Energy :: Thermal Energy is the Internal Energy stored in the system maintained at a certain Temperature.

An ideal habitat with unlimited resources is associated with Exponential growth.