Depends how you measure it. Any X kg/lbs of matter here on earth is still that same X kg/lbs everywhere in the universe. Assuming the scale being used to weight is correctly calibrated to whatever planet it's in, it would still show up as the same amount of kg/lbs.
This is why simple balances are such a brilliant idea despite their simplicity. You don't need to calibrate to the local conditions, if I have a 250g mass on one side, and I put something on the other side and it balances, that's 250 grams, done. Only the (often provided with the balance) prototype masses need to be calibrated and that can be done by experts far from your local environment.
Until as recently as 2019 this approach - using a prototype - was the only extant mass definition, the prototype kilogram lived at a specialised laboratory and its clones were used around the world to define mass (yes including the pound if you're an American).
[ Today instead the Planck constant is defined to be exactly 6.62607015×10^−34 kg x m^2 per second and it's possible to build devices such as a Kibble balance to estimate what the kilogram is from knowing this definition, the better your Kibble balance the better the estimate ]
Depends upon what you set out to measure. lbs is specifically a unit of force. kg is specifically a unit of mass. It is a category error to equate these as measures, although (in many places) an everyday convention to do so on Earth.
IIRC the English unit for mass is the slug. If the tecnical limit is 70lbs or so, that is must technically be read as lbs force -- aka force of gravity which varies with location.
Incorrect. The avoirdupois pound (lb) is historically a unit reflecting the long conflation of mass and force, but the modern unit of that name is expressly a mass unit that is a derived unit of the kilogram. The corresponding unit for force is the pound-force, (lbf).
If I remember right, given that free neutrons aren’t stable and have a very short half life, it would be explosively unwise even if it was physically possible.
Yes, a free neutron decays to a proton, an electron and an electron neutrino with a half life of 879 seconds. This decay releases 0.8MeV of energy (mostly in the form of kinetic energy of the electron).
My back of the envelope calculation shows that 1 gram of neutronium (approximately a mole) will release 43MW of energy continuously. Multiply that by 10^14 (the number of grams of neutronium per teaspoon) and the resultant energy release would be unimaginably huge. 'Explosively' does not even begin to describe it.