There are 2 Ca, 4 H (2*2) and 4 O (2+2) on the left hand side. So there should be the same number of atoms 2Ca and 4(O+H) on the right hand side. The reaction is a synthesis (making something new), rather than a decomposition (destroying something).
The answer is Two molecules of Ca(OH)2 should be produced during the synthesis reaction.
4, 2, 1, and 3 is the answer
Answer: 
Explanation: According to the law of conservation of mass, mass can neither be created nor be destroyed.
The mass of products must be same as that of the mass of reactants. For this the number of atoms of each element must be same on both sides of the arrow. Thus we need to balance the chemical equations.
Answer:
Vertebrae
Explanation:
Vertebrae are the 33 individual bones that interlock with each other to form the spinal column. The vertebrae are numbered and divided into regions: cervical, thoracic, lumbar, sacrum, and coccyx (Fig. 2). Only the top 24 bones are moveable; the vertebrae of the sacrum and coccyx are fused.
