When 46 grams of water are produced how many grams of oxygen must react according to the equation 2h2+o2=2h2o

the balanced equation for the formation of water is as follows

2H₂ + O₂ ---> 2H₂O

molar ratio of oxygen to water is 1:2

mass of water produced is - 46 g

therefore the number of moles of water produced - 46 g / 18 g/mol = 2.56 mol

1 mol of oxygen reacts to give 2 mol of water assuming oxygen is the limiting reactant

for 2 mol of water to be produced 1 mol of oxygen has to react

therefore for 2.56 mol of water to be produced - 1/2 x 2.56 mol = 1.28 mol of oxygen should react

mass of oxygen reacted is - 1.28 mol x 32 g/mol = 41.0 g

mass of oxygen that should react is 41 g

assuming that your periodic table has eighteen columns, you should highlight   the four elements in the third column from the left of the table.

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the have energy higher than those in the orbital while lower than those of the orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the orbital is therefore filled right after orbitals and before orbitals.  

potassium has electron configuration and calcium . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the and should be highlighted as well.