Double Slider Crank Chain:
The double slider crank chain is a mechanism that consists of two turning pairs and two sliding pairs. It is often used in various mechanical systems to convert rotary motion into reciprocating motion or vice versa. The mechanism is commonly found in engines, pumps, and other devices that require a back-and-forth motion.

Elliptical Trammel:
The elliptical trammel is a geometrical construction that involves two sliders connected by a rod. It is used to create an elliptical motion by manipulating the positions of the sliders. This mechanism is often employed in drafting and drawing instruments to create smooth and accurate elliptical shapes.

Scotch Yoke Mechanism:
The Scotch yoke mechanism is a type of mechanism that converts rotary motion into reciprocating motion. It consists of a slider connected to a rotating crank through a yoke. As the crank rotates, the slider moves back and forth in a straight line. This mechanism is widely used in engines, pumps, and other applications that require a linear reciprocating motion.

Explanation:
The given question states that the mechanism in which two are turning pairs and two are sliding pairs is called. The correct answer is option 'D' which states that all of the mentioned mechanisms (double slider crank chain, elliptical trammel, and Scotch yoke mechanism) fit the given description.

The double slider crank chain has two turning pairs, which are the connections between the crank and the connecting rod, and two sliding pairs, which are the connections between the connecting rod and the slider.

The elliptical trammel consists of two sliders connected by a rod. Although it does not have any turning pairs, it has two sliding pairs.

The Scotch yoke mechanism has one turning pair, which is the connection between the crank and the yoke, and one sliding pair, which is the connection between the yoke and the slider.

Therefore, all of the mentioned mechanisms have two turning pairs and two sliding pairs, making option 'D' the correct answer.

Overall, the question assesses the knowledge of different mechanical mechanisms and their characteristics. It is important for mechanical engineers to understand these mechanisms and their applications in order to design and analyze various machines and systems effectively.