The pH of lysosomes is 4.5. At this acidic pH, all the lysosomal enzymes are functional.

Lysosomes were discovered and named by Belgian biologist Christian de Duve, who received the Nobel Prize in physiology or medicine in 1974.

Studies on glucose-6-phosphate in 1949 led to serendipitous discovery of lysosomes. 

Enzymes of the lysosomes are synthesised in the rough endoplasmic reticulum.

Lysosome enzymes are specifically tagged with the molecule mannose 6-phosphate to differentiate them from other enzymes.

Macro-molecules undergo endocytosis by lysosomes.

The nuclear genes control the synthesis of lysosomal enzymes. Thus, mutations in genes for nucleus causes lysosomal storage diseases.

Leakage of the hydrolytic enzymes would have no effect on cytosolic organelles.

Vacuolar H+-ATPases are responsible for transport of protons from cytosol to lysosome for maintaining pH.

The late endosome itself can eventually grow into a mature lysosome.

Metachromatic leukodystrophy is a lysosomal storage disease that also affects sphingolipid metabolism. 

Gaucher's disease is the most common LSD caused due to the deficiency of the enzyme glucocerebrosidase.

Option 3 is correct.

Phenomenon of acid trapping or lysosomotropism is caused due to the accumulation of lipophilic weak bases in lysosomes.

Both animal lysosomes and some plant vacuoles perform autophagy.