**Core Concept**
The gallbladder is a small, pear-shaped organ that stores bile produced by the liver. On laparotomy, a healthy gallbladder should exhibit distinct characteristics due to its normal function and anatomy.

**Why the Correct Answer is Right**
A healthy gallbladder is typically "sea-green" in color due to its bile content. This coloration is a result of the bilirubin and bile salts present in the bile. The wall of a healthy gallbladder is also thin and elastic, allowing it to stretch and accommodate varying amounts of bile. This elasticity is crucial for the gallbladder's function of concentrating bile by storing and releasing it as needed.

**Why Each Wrong Option is Incorrect**
**Option A:** The color of the gallbladder is not always green; it can appear pale or yellowish in certain conditions, such as in the presence of a gallstone or after fasting.

**Option B:** While a healthy gallbladder wall is indeed thin, it is not necessarily elastic in the same way as other organs, such as the stomach or small intestine. The gallbladder's wall is more fibrous and contains a significant amount of smooth muscle.

**Option C:** A healthy gallbladder can be emptied, and its ability to do so is a critical aspect of its function in the digestive system. The gallbladder contracts to release bile into the bile ducts, which then carry it into the small intestine for fat digestion.

**Option D:** A healthy gallbladder is actually quite visible during laparotomy, especially when it is distended with bile or after the removal of nearby organs or adhesions.

**Clinical Pearl / High-Yield Fact**
A key feature of a diseased gallbladder is its loss of elasticity and the development of fibrosis, making it more rigid and less able to contract to release bile.

**Correct Answer: b) Wall is thin & elastic.**