Hydrogen

Melting point :−259.2 °C(lit.)
Boiling point :−252.8 °C(lit.)
Density :0.0899
vapor density :0.07 (21 °C, vs air)
vapor pressure :Critical temperature is - 239.9 °C; noncondensible above this temperature
Flash point :<-150°C
solubility :slightly soluble in H2O
pka :35(at 25℃)
form :colorless gas
color :colorless gas; flammable
Odor :Odorless gas
explosive limit :74.2%
Water Solubility :0.00017 g/100 mL
Merck :13,4813
Dielectric constant :1.0（100℃）
Stability :Stable. Highly flammable. Readily forms explosive mixtures with air. Upper (U.K.) composition limit for use of a nitrogen/hydrogen mixture in the open lab is 5.7% hydrogen.
CAS DataBase Reference :1333-74-0(CAS DataBase Reference)
NIST Chemistry Reference :Hydrogen(1333-74-0)
EPA Substance Registry System :Hydrogen (1333-74-0)

Symbol(GHS):
Signal word:	Danger
Hazard statements:	Code Hazard statements Hazard class Category Signal word Pictogram P-Codes H220 Extremely flammable gas Flammable gases Category 1 Danger P210, P377, P381, P403 H280 Contains gas under pressure; may explode if heated Gases under pressure Compressed gas Liquefied gas Dissolved gas Warning P410+P403
Precautionary statements:	P210 Keep away from heat/sparks/open flames/hot surfaces. — No smoking. P377 Leaking gas fire: Do not extinguish, unless leak can be stopped safely. P381 Eliminate all ignition sources if safe to do so. P410+P403 Protect from sunlight. Store in a well-ventilated place.