What is the force that can cause two pieces of iron to attract each other?
a.
gravitational force
b.
magnetic force
c.
elastic force
d.
electrostatic force

B. Magnetic Force

Explanation:

two pieces of irons cannot attract each other unless at least one of them is magnetize. That force is called magnetism.

Is it A ?  Yes !  Two pieces of iron DO always attract each other with equal and opposite gravitational forces, although the forces are so small that we never notice them.

Is it B ?  Yes, it could be.  If at least one of the pieces of iron is magnetized, then they can attract each other with equal and opposite magnetic forces.

Is it C ?  Yes, it could be.  But the pieces of iron would have to be joined by a stretched rubber band.  Then they would attract each other with equal and opposite elastic forces.

Is it D ?  Yes, it could be.  If one of the pieces of iron carries a net electric charge, then they attract each other with equal and opposite electrostatic forces.  

the first, second, and fifth options

answer: 802.3 kilo joules of energy represents 191.75 kilo calorie of energy.

explanation:

energy released during combustion of one mole methane = 802.3 kilo joules

if 1 kilo joule = 0.239006   kilo calorie

then ,802.3 kilo joule will be = 802.30.239006 kilo calorie

802.3 kilo joule = 191.75 kilo calorie

hence, the energy in kilo calorie is 191.75 kilo calorie.