How to remember the first 20 elements of the periodic table?

Hi.

You can use mnemonics. I found this in the internet:

Happy Henry Beside Boron Cottage, Near Our Friend Nelly Nancy Mg Allen. Silly Patrick Stays Close. Arthur Kisses Carrie.

Mg- magnesium by the way

answer: semi-infinite solid initially at a uniform temperature of 400 ◦c is cooled at its surface by convection. the cooling fluid at a constant temperature of 200 ◦c has a convective coefficient (ha) of 250 w/m2.k. the physical properties of the solid: k = 20 w/m.k and α = 4 * 10-5  m2/s. using δx = 0.04 m and δt = 10 s. write the finite difference equations describing the transient heat transfer of the first five δx and the temperature profile after 30 s.