# PTE Reading MCM #10: Principles and Applications...

Reading: Multiple Choice, Multiple Answers #10 - Level 2 - Feeds Reading

> Read the text and answer the question by choosing all the options that are correct. More than one answer is correct, and a wrong choice costs a point.

X-ray crystallography is the study of crystal structures through X-ray diffraction techniques. When an X-ray beam bombards a crystalline lattice in a given orientation, the beam is scattered in a definite manner characterized by the atomic structure of the lattice. This phenomenon, known as X-ray diffraction, occurs when the wavelength of X-rays and the interatomic distances in the lattice have the same order of magnitude. In 1912, the German scientist Max van Laue predicted that crystals exhibit diffraction qualities. Concurrently, W. Friedrich and P. Knipping created the first photographic diffraction patterns. A year later, Lawrence Bragg successfully analyzed the crystalline structures of potassium chloride and sodium chloride using X-ray crystallography and developed a rudimentary treatment for X-ray/crystal interaction (Bragg's Law). Bragg's research provided a method to determine the number of simple crystal structures for the next 50 years. In the 1960s, the capabilities of X-ray crystallography were greatly improved by the incorporation of computer technology. Modern X-ray crystallography provides the most powerful and accurate method for determining single-crystal structures. Structures containing 100-200 atoms now can be analyzed in the order of 1-2 days, whereas before the 1960s a 20-atom structure required 1-2 years for analysis. Through X-ray crystallography, the chemical structure of thousands of organic, inorganic, organometallic, and biological compounds are determined every year.

Which of the following factors are consistent with the theory of X-ray crystallography?

- X-ray crystallization causes a reduction in the interatomic distances of wavelengths
- X-rays are scattered according to the atomic structure of the crystal lattice.
- The analysis of chemical compounds was only possible after the development of computer technology.
- The process can be used to determine the chemical structure of biological compounds.
- X-rays will not detract from crystalline substances.

## Answer

- X-rays are scattered according to the atomic structure of the crystal lattice.
- The process can be used to determine the chemical structure of biological compounds.

## Explanation

The text explicitly states that the beam is scattered based on the lattice structure and confirms the technique is used for biological compounds.

What to watch: The beam is "scattered in a definite manner" set by the lattice's atomic structure. The method also finds structures of "biological compounds" every year. The computer option is tempting, but Bragg analyzed salt crystals in 1913, before computers. Computers only made analysis faster. Nothing says distances shrink.

## Hints

- Look for sentences mentioning how X-rays interact with crystal lattices.
- Check the final sentence of the passage to see what types of compounds are analyzed.

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