Short answers, pulled from the story.
Transliteration converts the written form of a word from one script to another, preserving spelling conventions rather than changing pronunciation. Transcription, by contrast, seeks to capture the actual sounds of a word, typically using the International Phonetic Alphabet or phonetic approximations in the target script.
The Arabic letter qaf represents a sound produced at the uvula rather than the soft palate, and its pronunciation varies across Arabic dialects. In some dialects it becomes a hard "g", in Egypt it is silent, and in formal literary Arabic it is most often rendered as "q" or occasionally "k" in English transliteration.
Systematic transliteration is a one-to-one mapping from one writing system to another, typically at the level of individual graphemes. When a system is one-to-one, a reader who knows the rules can reconstruct the original spelling exactly. Examples of named systematic systems include the Wylie transliteration for Tibetan, the International Alphabet of Sanskrit Transliteration, and Buckwalter transliteration for Arabic.
The Russian letter Kha, written as "X" in Cyrillic, represents a voiceless velar fricative sound, the same consonant as the Scottish "ch" in "loch". Because that sound does not exist in most forms of English, transliterators represent it as "kh", giving the spelling "Khrushchev" as an approximation of the original Russian pronunciation.
By convention, angle brackets are used to set off transliterations, while slashes mark phonemic transcription and square brackets mark phonetic transcription. However, the source notes that conventions and author preferences vary, so these markers are not universally applied.
Pinyin is the official romanization of Chinese. Other systems also exist, including Cyrillization of Chinese and Bopomofo, but Pinyin is the standard recognized system for converting Chinese characters into Latin-script spelling.