A. If the Committee has not mandated that you use a ball from the List of Conforming Golf Balls, you may use a practice or X-Out golf ball. When employing an X-Out ball in this situation, if there is solid proof that the ball does not conform, the ball should not be utilized.
B. Yes, provided it has not been "marked" with some type of identification mark (i.e., name, number). Such a marked ball cannot be used in any sanctioned event and should be disposed of properly.
C. No, a practice golf ball is for training only. It can't be used in competition because its performance will be affected by weather conditions, how long it's been since your last time out on the course, etc.
D. A practice golf ball is just that - a practice golf ball. It is not designed to meet ANSI/R&F standards for distance, but rather for bettering one's game through practice. Training balls come in many different shapes and sizes so they can be used for various types of training exercises.
E. No, you cannot use a practice ball in competition. It could affect the outcome of your match/round in ways such as giving you an unfair advantage due to familiarity effects.
There is no one correct response to this issue since the usage of these non-conforming balls is more of a personal choice among golfers than a rule. You should not utilize these balls in tournaments or when money is at stake, but otherwise, have at it. It is your call on how to play the game.
Non-conforming golf balls are defined as any ball that was not designed for use by humans. This includes balls such as glow-in-the-dark balls, balls with symbols printed on them, and even balls with animals names such as Piglet or Snoopy. These balls may be fun to play with personally, but they will not conform to the rules of golf and thus are not legal for use with a golf club.
Golf clubs were originally made from wood, which can break if hit with too much force. Thus, the game was invented - a contest played with a ball and a stick! - because wooden clubs were too dangerous. In 1885, Benjamin John Cunningham developed the first rubber ball. Before then, balls had been made from gutta-percha or leather.
This means that if you use a non-conforming ball, your opponent will be given permission to do so too.
Golf balls, like golf clubs, are subject to testing and approval by the R & A (previously the Royal and Ancient Golf Club of St Andrews) and the United States Golf Association, and any that do not adhere to standards are not permitted to be used in competitions (Rule 5-1). Balls may also be disqualified if they have been altered in any way or are found to be defective. In this case, an alternate ball must be provided or play will be halted.
In the early days of golf, when equipment was less consistent and reliable, balls were sometimes made from skins - the outer layer of an animal's head. These were often black but other colors were also used. The inner core was usually a rubber ball about the same diameter as a modern golf ball. These balls could be played for many hours because the skin would split and dry out if it wasn't hit sufficiently hard.
The first manufactured golf ball was called a "Nipon" and was introduced into Japan in 1872. It consisted of a leather cover wrapped around a steel ball covered in gutta percha (now known as styrene butadiene rubber or SBR). Around 1900, more durable synthetic materials were developed for use in golf balls, including china clay for Wainwright and Dunhill brands, and sulfur for Boody Ball. In the 1950s, polyurethane became popular for use as a cover material.